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Cleavage with cyanogen bromide was employed to investigate the N-terminal amino acid sequence of the λ-chains of normal porcine immunoglobulin. The N-terminal homoserine-containing nonapeptide was isolated from all fractions of the λ-chains in a yield of 60% of theory. Its amino acid sequence was determined by mass spectrometry and was found to be uniform. Other homoserine-containing fragments were obtained from the cyanogen bromide hydrolyzate of the λ-chains with split disulfide bonds. Partial amino acid sequence of these fragments provided evidence that methionine in position 9 is present in more than 60% of variants and obviously has an invariant character. Variants of the λ-chains exist (by estimate not more than 15% of the total λ-chains) which, in addition to the invariant methionine residue in position 9, possess a variable methionine residue in the section between positions 46 and 51. The data obtained indicate that the sequence of 23 amino acid residues from the N-terminus of porcine λ-chains is uniform with the exception of a single replacement (in position 13). Moreover, in comparison with the sequence of λ-chains of man, mouse and birds, the sequence displays several species-specific replacements and a deletion of threonine which occupies position 5 in the chains of the other species. In the pig, the λ-chains represent the predominant type of light chains (some 70%). Hence it follows that some 50% of the light chains in this species possess a uniform amino acid sequence in the N-terminal section. These facts are difficult to reconcile with the germline theories of genetic control so that mechanisms of somatic diversification of immunoglobulins must be envisaged.

Two nonadeoxynucleotides with the sequences, d-C-T-A-A-G-G-G-A-G (nonanucleotide-I) and d-T-C-T-C-C-G-G-T-T (nonanucleotide-II), and a heptadeoxynucleotide having the sequence, d-A-G-A-G-T-C-T, have been chemically synthesized. These polynucleotides represent, respectively, the nucleotide sequences 22 to 30, 41 to 49, and 28 to 34 of the gene for yeast alanine transfer RNA (Fig. 1). The synthetic steps used in the synthesis of the nonanucleotide-I were: the condensation of the protected nucleoside, d-MMTr-C An , with the protected nucleotide, d-pT- O Ac, to give the dinucleotide, d-MMTr-C An pT; the condensation of the dinucleotide with d-pA Bz - O Ac to give the trinucleotide, d-MMTr-C An pTpA Bz ; the condensation of the latter with the dinucleotide, d-pA Bz pG 1B- O Ac, to give the pentanucleotide, d-MMTr-C An pTpA Bz pA Bz pG 1B ; the condensation of this pentanucleotide with d-pG 1B pG 1B - O Ac to give the protected heptanucleotide, d-MMTr-C An pTpA Bz pA Bz pG 1B pG 1B pG 1B , and finally, the condensation of this heptanucleotide with the dinucleotide, d-pA Bz pG 1B - O Ac, to give the protected nonanucleotide, d-MMTr-C An pTpA Bz pA Bz pG 1B pG 1B pG 1B pA Bz pG 1B . The steps used in the synthesis of the nonanucleotide-II were: the condensation of d-MMTr-T with the tetranucleotide, d-pC An pTpC An pC An - O Ac, to give the pentanucleotide, d-MMTr-TpC An pTpC An pC An ; the condensation of the latter with the dinucleotide, d-pG 1B pG 1B - O Ac, to give the heptanucleotide, d-MMTr-TpC An -pTpC An pC An pG 1B pG 1B , and finally, the condensation of the heptanucleotide with the dinucleotide, d-pTpT- O Ac, to give the protected deoxynonanucleotide, d-MMTr-TpC An pTpC An pC An pG 1B pG 1B pTpT. For the synthesis of the heptanucleotide, A-G-A-G-T-C-T, the 5′-monocyanoethyl tetranucleotide, d-CEpA Bz -pG 1B pA Bz pG 1B , was condensed with the trinucleotide, d-pTpC An pT- O Ac, to give the protected heptanucleotide, d-pA Bz pG 1B pA Bz pG 1B pTpC An pT. After removal of the N -protecting groups, the completely deprotected nonanucleotides, as well as the intermediate oligonucleotides and the heptanucleotide, d-A-G-A-G-T-C-T, were purified further by a combination of paper and column chromatography.

Mouse A9 cells, deficient in hypoxanthine phosphoribosyltransferase (EC 2.4.2.8), were fused with normal chick erythrocytes and selected in hypoxanthine-aminopterin-thymidine medium for cells with hypoxanthine phosphoribosyltransferase activity. Recovered hybrid cells produced the chick hypoxanthine phosphoribosyltransferase exclusively, as demonstrated by electrophoretic mobility and immunoprecipitation tests, even though no chick chromosomes or chick cell-surface antigens could be identified in the hybrids. Surprisingly, the expression of the chick hypoxanthine phosphoribosyl-transferase activity in the mouse/chick hybrids required the presence of aminopterin in the growth medium; in its absence, enzyme synthesis decreased markedly. Because of the rapid and reversible modulation of hypoxanthine phosphoribosyltransferase activity, the hybrid cells could proliferate equally well in media containing hypoxanthine-aminopterin-thymidine or 8-azaguanine. Cellular selection was definitely ruled out as a possible cause. These results confirm previous reports that specific genetic information can be selectively transferred from one cell to another of a distant species. Furthermore, they demonstrate that an avian gene, whose activity is normally expressed constitutively, can become facultative when integrated into a mammalian cell. This seems to be the first instance where heterologous gene activity has been shown to be reversibly modulated in hybrid cells.

Homogeneous main band DNA was isolated from total human DNA by Hg2+-Cs2 SO4 and neutral CsCl density gradients. This DNA fraction contained approximately 15% of the DNA sequences, banded at 1.696 g/cm3 in CsCl, had a molecular weight of 11.5 · 106 and had a G + C content of 37% in comparison to total DNA which was found to be 40%. Characterisation of this DNA fraction by reassociation kinetics showed that it was not a high molecular weight intermediate DNA fraction nor was it enriched with intermediate DNA sequences over the proportion present in total human DNA. An enrichment in fast fraction sequences, however, suggested that a satellite DNA was present in this fraction. From further experimentation it became clear that a large proportion of DNA sequences isolated as homogeneous main band DNA were isolated as artefacts of the fractionation procedure. Satellite DNA sequences constitute 10% or more of this DNA fraction. It is suggested that they correspond to human DNA satellite III and are to be located on the light side of Hg2+—Cs2 SO4 gradients.

We have determined the genetic complexity of mtDNA from Euglena gracilis, var. bacillaris, by DNA renaturation experiments. Renaturation was followed by the specific digestion of single-stranded DNA with nuclease S1. The complexity found with this method is about 40 · 106, i.e. in the range reported for some other unicellular eukaryotes. The molecular weight of 3–4 · 106, reported by others for Euglena mtDNA therefore does not reflect its genetic information content.

The 5′-terminal sequence of mRNA from the galactose operon of E. coli has been determined. gal RNA is synthesized in vitro by means of a kinetically controlled purified transcription system and is isolated by a two-step RNA·DNA hybridization scheme. The following sequence of the first 77 nucleotides has been deduced by analysis of oligonucleotides produced by digestion with T 1 , pancreatic, and carboxymethylated pancreatic ribonucleases: ppA-U-A-C-C-A-U-A-A-G-C-C-U-A-A-U-G-G-A-G-C-G-A-A-U-U-A-U-G-A-G-A-G-U-U-C-U-G-G-U-U-A-C-C-G-G-U-G-G-U-A-G-C-G-G-U-U-A-C-A-U-U-G-G-A-A-G-U-C-A-U-A-C-C-U-G-U. Residues 27-77 correspond to the amino terminal 17 amino acids of UDPgalactose 4-epimerase (EC 5.1.3.2), the protein specified by the promoter-proximal structural gene of the operon. A self-complementary sequence occurs near the 5′ terminus; 12 of 15 nucleotides between residues 4 and 18 are symmetrically located about position 11. The sequence of residues 22-33 closely resembles part of the lactose operator sequence reported previously [Gilbert, W. & Maxam, A. (1973) Proc. Nat. Acad. Sci. USA 70, 3581-3584].

The decadeoxynucleotides, d-T-C-G-G-T-A-G-C-G-C and d-T-G-G-C-G-C-G-T-A-G, corresponding to the nucleotide sequence 51 to 70 of one of the strands, and d-[ 14 C]A-C-C-G-A-C-T-A-C-G, corresponding to the nucleotide sequence 56 to 65 of the complementary strand of the gene for the major alanine tRNA from yeast have been synthesized. The synthesis of the decanucleotide, d-T-C-G-G-T-A-G-C-G-C, started with the condensation of 5′- O -monomethoxytrityldeoxythymidine, d-MMTr-T, with 3′- O -acetyl- N (6) -anisoyldeoxycytidine 5′-phosphate (d-pC An - O Ac) to give d-MMTr-TpC An . Successive condensations with d-pG 1B - O iB, d-pG 1B - O iB, d-pTpA BZ pG 1B - O Ac and d-pC An pG 1B pC An - O Ac followed by removal of the protecting groups produced the decanucleotide. The synthesis of the decanucleotide, d-[ 14 C]A-C-C-G-A-C-T-A-C-G, started with the condensation of 5′- O -monomethoxytrityl- N (6) -benzoyl-[8- 14 C]deoxyadenosine (d-MMTr-[ 14 C]A BZ ) with 3′- O -acetyl- N (6) -anisoyldeoxycytidine 5′-phosphate to give d-MMTr-[ 14 C]A BZ pC An . Successive condensations with d-pC An pG 1B - O Ac, d-pA BZ pC An - O Ac, d-pTpA Bz - O Ac and d-pC An pG 1B - O Ac, followed by the removal of the protecting groups, produced the decanucleotide. The synthesis of the decanucleotide, d-T-G-G-C-G-C-G-T-A-G, started with the condensation of 5′- O -monomethoxytrityldeoxythymidine, d-MMTr-T, with N ,3′- O -di-isobutyryldeoxyguanosine 5′-phosphate, d-pG 1B - O iB, to give d-MMTr-TpG 1B . Successive condensations with d-pG 1B - O iB, d-pC An - O Ac, d-pG 1B - O iB,d-pC An pG 1B - O iB and d-pTpA BZ pG 1B - O Ac produced the decanucleotide. The condensing agent used throughout was mesitylenesulfonyl chloride. Isolation of the fully protected oligonucleotide products after every condensation was accomplished by using solvent extraction procedures and/or anion exchange chromatography. The fully deprotected products, d-T-C-G-G-T-A-G-C-G-C, d-[ 14 C]A-C-C-G-A-C-T-A-C-G, and d-T-G-G-C-G-C-G-T-A-G, were further purified by anion-exchange chromatography on a DEAE-cellulose columns in the presence of 7 M-urea and were characterized by enzymic degradation to the constituent nucleosides and nucleotides.

Human blood group O cells were converted to B-active cells by incubation with uridine diphosphate d-galactose and enzyme preparations from group B stomach mucosa or serum from group B or AB subjects. The specificity of the converted cells was tested by their reaction with human and rabbit anti-B sera and by the specific inhibition of the newly acquired agglutinating properties by soluble blood group B substance and B-active oligosaccharides. The failure of the α-galactosyltransferases to transform cells of the ‘Bombay’ Oh phenotype into B-active cells supports the concept that H-active structures are the acceptors of the transferred galactosyl residues.

Mutants of Escherichia coli K-12 blocked in each of the three enzymatic reactions between chorismate and 2,3-dihydroxybenzoate, in the pathway leading to the iron-sequestering compound enterochelin, have been isolated and biochemically characterized. The three genes concerned (designated entA, entB and entC ) have been shown to be clustered on the chromosome between purE and gal and to be located near minute 14 by cotransduction with the purE, lip , and fep genes. entA, entB , and entC were shown to be the structural genes for 2,3-dihydro-2,3-dihydroxybenzoate dehydrogenase, 2,3-dihydro-2,3-dihydroxybenzoate synthetase, and isochorismate synthetase, respectively.

Several diaminopimelic acid (DAP)- and lysine-requiring mutants of Escherichia coli were isolated and studied by genetic, physiological, and biochemical means. The genes concerned with DAP-lysine synthesis map at several different sites on the E. coli chromosome and, therefore, do not constitute a single operon. Three separate loci affecting DAP synthesis are located in the 0 to 2.5 min region of the genetic map. The order of the loci in this region is thr-dapB-pyrA-ara-leu-pan-dapC-tonA-dapD . Two additional DAP genes map in the region between min 47 and 48, with the gene order being gua-dapA-dapE-ctr . The lys locus at min 55 determines the synthesis of the enzyme DAP decarboxylase, which catalyzes the conversion of DAP into lysine. The order of the genes in this region is serA-lysA-thyA .

I F selection operates independently on each locus, its action on the large amounts of genic variability discovered in many populations (e.g., LEWONTIN and HUBBY 1966) would cause excessive genetic loads compared with the actual situation. In order to accommodate selection for many genes, threshold or truncationselection models have been proposed assuming heterozygote superiority ( SVED, REED and BODMER 1967; KING 1967; MILKMAN 1967; WILLS, CRENSHAW and VITALE 1970). As a typical form, MILKMAN and WILLS et al. assumed that the individuals having the largest number of heterozygous loci are selected to produce the next generation. Selection acts at the phenotypic level, the phenotype being the result of genotypic and environmental (including chance) effects. Thus. for any trait including fitness. large phenotypic values do not always follow from large genotypic values. We have attempted to examine the genetic consequences of the typical phenotypic truncation selection on the basis of the genetic parameters for viability obtained in D. melanogaster. If this truncation-selection occurs, it is probably operating mainly in the period from egg to adult. We have estimated the genotypic and environmental variances, and the heritability (broad sense) of egg-adult viability. Two experiments were conducted, one to estimate the variability in relative viability and the other to estimate mean viability. Employed were second chromosomes from 691 extracted by the marked inversion technique from a population in a state park near Raleigh, North Carolina. This population is probably near equilibrium (MUKAI et al. 1971 ) . To estimate variability, the relative viabilities of 688 random heterozygotes were estimated using the Cy method (cf. WALLACE 1956). Crosses were made between five Cy/+i females and five CY/+^+^ males (between successively numbered lines where the subscript indicates line number), and Cy is SMI ( C y ) . Four days after the crosses were made, all flies were transferred to the second vial for another four days and then discarded. The numbers of C y and of wild-type flies of each pair of vials were pooled, and the relative viability of heterozygous wild

A decadeoxynucleotide, d-G-G-A-G-C-G-C-G-C-T, and a dodecadeoxynucleotide, d-C-T-A-C-C-G-A-C-T-A-C-G, which represent, respectively, the nucleotide sequences 46 to 55 and 54 to 65 of one of the strands of the gene corresponding to yeast alanine transfer RNA (Fig. 1) have been chemically synthesized. The steps involved in the synthesis of the decanucleotide (segment 10, Fig. 1) were: the condensation of d-MMTr-G 1B pG 1B with d-pA BZ pG 1B - O Ac to give the tetranucleotide, d-MMTr-G 1B pG 1B pA BZ pG 1B , then successive condensations of the tetranucleotide with the appropriate mononucleotides to give the hexanucleotide, d-MMTr-G 1B pG 1B pA Bz -pG 1B pC An pG 1B and the condensation of the hexanucleotide first with d-pC An pG 1B - O Ac and then with d-pC An pT- O Ac to give the protected decanucleotide, d-MMTr-G 1B pG 1B pA BZ pG 1B pC An pG 1B pC An pG 1B pC An pT. The steps involved in the synthesis of the dodecanucleotide (segment 12′, Fig. 1) were: the successive condensations of d-MMTr-C An pT with d-pA BZ pC An - O Ac, d-pC An pG 1B - O Ac and d-pA BZ pC An - O Ac to give the octanucleotide, d-MMTr-C An pTpA BZ pC An pC An pG 1B -pA BZ pC An , and the condensation of the octanucleotide with d-pTpA BZ pC An pG 1B - O Ac to give the dodecanucleotide, d-MMTr-C An pTpA BZ pC An pC An pG 1B pA BZ pC An -pTpA BZ pC An pG 1B . The purification and characterization of the completely unprotected deoxypolynucleotides are described.

Some of the properties of three metK mutants of Escherichia coli K-12 have been examined. All three strains have lower than normal levels of SAM (S-adenosyl-l-methionine) synthetase and elevated levels of cystathionine synthetase and cystathionase. One strain (RG73) appears to have an unstable SAM synthetase, suggesting that it carries a structural gene mutation. The two strains (RG62 and RG109) which have the lowest levels of SAM synthetase when grown on minimal medium have appreciably higher levels of enzyme when grown on complete medium. Growth on defined media supplemented with leucine or methionine causes a several-fold increase in the specific activity of SAM synthetase with associated decreases in cystathionine synthetase and cystathionase, but the changes are not as large as those seen in cells grown on LB broth. The SAM pools of strains RG62 and RG109 are markedly lower than normal while that of strain RG73 is slightly below normal. The methionine pools of all three strains are elevated several-fold. The metK strains are able to synthesize cyclopropane fatty acids, but the rate of their formation is slowed. Modification and restriction of phage 21 appears to be normal, suggesting that these strains are able to methylate DNA.