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We have analyzed more than 500 alphoid monomers either sequenced in our laboratory or available in the literature. Most of them belonged to the well studied suprachromosomal families 1, 2 and 3 characterized by dimeric (1 and 2) and pentameric (3) ancestral periodicities. The sequences that did not belong to the previously known families were subjected to further analysis. About a half of them formed a relatively homogenous family. Its members were on average 80.5% identical and 89.5% homologous to the M1 consensus sequence derived from this group (39 monomers). In the genome they do not form any ancestral periodicities other than a monomeric one, and are found at least in chromosomes 13, 14, 15, 21, 22 and Y. The newly defined family was termed suprachromosomal family 4. Comparison of all 10 alphoid monomeric groups identified so far showed that the M1 sequence is closely related to the J1-D2-W4-W5 homology grouping. Notably the African Green Monkey alpha satellite, also characterized by monomeric construction, appears to be a member of the same group.

Somatic and oocyte 5S rRNAs from the liver and unfertilized eggs of the loach (Misgurnus fossilis have been sequenced and found to differ in six nucleotides. All the substitutions are confined to the 5'-half of the molecules; 4 of them are pyrimidine-pyrimidine substitutions, and 2 are purine-pyrimidine ones. Considerable differences, both in the position and the character of substitutions, have been established when these 5S rRNAs were compared with somatic and oocyte 5S rRNAs from Xenopus borealis and Xenopus laevis. Among the known primary structures, somatic 5S rRNA of M. fossilis is most similar to trout 5S rRNA.

A version of rapid gel sequencing procedure based on the analysis of partial endonuclease hydrolizates of chemically modified 5'-32P-labelled RNA is suggested. Complete and selective modification of cytidilic residues by a methoxyamine-bisulfite mixture leads to the unfolding of the RNA secondary structure and, due to this effect, to the generation of a more uniform set of fragments after partial RNAase hydrolysis. The position of cytidines in an RNA sequence can be determined by restricting the hydrolysis of phosphodiester bonds between the modified CMP residues and their 3'-neighbours with T2 and A RNAases. The method was verified with tRNATrp (yeast) and 5S RNA (rat liver and yeast).

We have studied the accessibility of 5'- 32P labeled oocyte and somatic 5S rRNAs from the fish Misgurnus fossilis L. to S1, T1 and cobra venom nucleases and have found that the cleavage sites of 5S rRNAs closely related in primary structures differ in these molecules. The data of nuclease hydrolyses revealed the existence of two conformers corresponding to renatured and partially denatured somatic 5S rRNA and capable of mutual interconversions. The exposed cytosine residues were located in oocyte and somatic 5S rRNAs converted into uridine ones by sodium bisulfite treatment. The data have been used to construct the secondary structure models of somatic and oocyte 5S rRNAs by means of specially devised computer program. These models differ in their 5'-halves which contain all the nucleotide substitutions in the primary structure, all differences in location of the exposed cytosine residues, and finally, in the cleavage pattern by the nucleases used.