Search

A large fraction of the genome of the lepidopteran Antheraea pernyi consists of interspersed single-copy sequences and repetitive DNA sequences of 300 nucleotide average length. Most of the single-copy sequences are about 800 nucleotides long and a minority are considerably longer. Thus, the organization of the DNA sequences of this insect is similar to that of most higher organisms and different from that of Drosophila.

Southern transfer and solution hybridization experiments, using as probe a DNA fragment that encodes for Drosophila actin, demonstrate cross hybridization to DNA from the sea urchin Strongylocentrotus purpuratus. Recombinant DNA clones that contained sea urchin genomic DNA fragments were constructed and screened for the presence of actin-encoding DNA sequences by colony hybridization with the Drosophila actin sequence. Two different putative actin-encoding clones were identified and were shown to specifically hybridize actin-encoding mRNA from a complex mRNA population. Southern blot hybridization experiments with both the Drosophila actin sequence and one of the cloned sea urchin sequences, in conjunction with solution hybridization data, suggest an actin gene copy number of 5-20 per haploid genome. DNA sequence analysis of one of the cloned sequences indicates that this fragment codes for a cytoplasmic form of actin and contains an intervening sequence of at least 200 nucleotides beginning immediately after amino acid 121 in the protein sequence.

RNA complementary to bulk humanplacental DNA was synthesized in vitro both in the presence and absence of (3)H-labeled ribonucleotides. The (3)H-labeled RNA was used directly for hybridization to the DNA of human metaphase chromosomes, whereas the unlabeled complementary RNA was labeled chemically with (125)I before hybridization. A comparison of autoradiographs produced by either isotope revealed no qualitative differences in the chromosomal annealing sites of the same population of RNA molecules. Since (125)I-labeled nucleic acids give similar, if not identical, results as do (3)H-labeled nucleic acids in in situ hybridization experiments, their use should make possible the localization of genetic elements for which tritium labeling methods are either inadequate or not possible.