In situ hybridization of cRNA transcribed from cloned D. melanogaster heat shock sequences to D. hydei chromosomes has shown that the D. hydei locus 2--32 A corresponds to the D. melanogaster locus 87 A/C and the D. hydei locus 2--36 A to the D. melanogaster locus 95 D, while the D. hydei locus 4--81 B corresponds to the D. melanogaster locus 63 BC. No hybridization to D. hydei chromosomes was found with cRNA transcribed from a clone containing the alpha beta sequences encoded by the D. melanogaster locus 87 C. Neither D. melanogaster heat shock RNA nor D virilis heat shock RNA hybridized significantly to the D. hydei heat shock locus 2--48 B. Furthermore, D. hydei heat shock RNA did not hybridize to the cytological homologs of locus 2--48 B found in D. repleta or in D. virilis. D. hydei heat shock. RNA did hybridize to the cytological homologs of locus 2--48 B in D. neohydei and D. eohydei, both of which belong to the hydei subgroup.

Transcription mapping was performed in the short region of the feline herpesvirus type 1 (FHV-1) genome as a first approach to the functional analysis of open reading frames encoding the homologs of the herpes simplex virus type 1 (HSV-1) gD, gl, gE, US9, and probably also US8.5. All reading frames appeared to be transcribed. Transcripts were grouped into two nested RNA sets; namely, the coterminal transcripts of gD and gl and the coterminal transcripts of gE, US8.5, and US9. This situation was similar to that found in the equivalent region of HSV-1. The FHV-1 ORFs US8.5 and US9 have not been described previously. Sequence analysis and comparison of the putative polypeptide encoded by US8.5 revealed that this ORF was unique to FHV-1. However, US8.5 of FHV-1 might be functionally related to its positional homologs in HSV-1 and equine herpesvirus type 1. In all three viruses, US8.5 does not seem to be critical for virus propagation in cell culture. This was shown for FHV-1 by isolating a mutant containing an insertion in US8.5 and comparing its growth properties in cell culture to those of the parent virus G2620. With regard to US9, conscientious amino acid sequence alignment of FHV-1 US9 and homologs in related herpesviruses suggests that this particular protein could contribute to the virus infectivity in vivo. This speculation was based on the highly conserved C-terminus of US9, starting with a characteristic YYSES motif and followed by a nuclear target sequence and a transmembrane region.

Four cell lines have been isolated from Drosophila hydei embryos. Three lines have a normal XY karyotype, the fourth has an XO karyotype with an additional small heterochromatic fragment. The cells contain presumable cytoplasmic virus like particles.

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Fluorochrome-labeled RNA allows the rapid detection of in situ hybrids without the need for long exposure times as in the autoradiographical hybridisation methods. Resolution is high because of the high resolving power of fluorescence microscopy. The application of a previously reported method for the hybrido-cytochemical detection of DNA sequences to polytene chromosomes of Drosophilia is described. The specificity and sensitivity of the method are demonstrated by the hybridisation with polytene chromosomes of 1) rhodamine-labeled 5S RNA, to the 5S rRNA sites of D. melanogaster (56F) and D. hydei (23B), 2) rhodamine-labeled RNA complementary to a plasmid containing histone genes, to the 39DE region of D. melanogaster, 3) rhodamine-labeled D. melanogaster tRNA species (Gly-3 and Arg-2), to their respective loci in D. melanogaster, 4) rhodamine-labeled RNA complementary to the insert of plasmid 232.1 containing part of a D. melanogaster heat shock gene from locus 87C, to D. hydei heat shock locus 2-32A. In the latter instance it was possible to demonstrate the labeling of a double band which escaped unambiguous detection by autoradiography in the radioactive cytochemical hybridisation procedure because of the low topological resolution of autoradiograms. The sensitivity of the fluorochrome-labeled RNA method is compared with the radioactive methods which use 3H- or 125 I-labeled RNAs. The factors governing the sensitivity and the number of bound fluorochrome molecules to be expected are discussed.