Electron microscopic analysis of the banding pattern in the salivary gland chromosomes of Drosophila melanogaster: divisions 37, 38 and 39 of 2L

The faint band/interband region 28C2 to 28C4-5(-) of the Drosophila melanogaster salivary gland polytene chromosomes is rich in transcripts

Urate oxidase mRNA and five other transcripts map along 38 kb of DNA in the region 28C on the Drosophila melanogaster second chromosome. Three biotinylated restriction fragments from this 38 kb of DNA, one from each end and one from the middle, were individually hybridized in situ to slightly stretched salivary gland polytene chromosomes. The data from these in situ hybridizations in combination with the transcription map of the 38 kb of DNA indicate that: (i) there are six discrete RNA species encoded along the 38 kb of DNA and (ii) these six transcripts map to the faint band/interband region which includes the proximal edge of 28C1, the three faint bands, 28C2, 28C3 and 28C4-5(-), and the adjacent interband chromatin. Our data are consistent with the few published studies directly demonstrating that faint band/interband regions of the Drosophila melanogaster salivary gland polytene chromosomes code for a high density of transcripts.

Isolation and characterization of the dopa decarboxylase gene of Drosophila melanogaster

We have isolated chromosomal deoxyribonucleic acid clones containing the Drosophila dopa decarboxylase gene. We describe an isolation procedure which can be applied to other nonabundantly expressed Drosophila genes. The dopa decarboxylase gene lies within or very near polytene chromosome band 37C1-2. The gene is interrupted by at least one intron, and the primary mode of regulation is pretranslational. At least two additional sequences hybridized by in vivo ribonucleic acid-derived probes are found within a 35-kilobase region surrounding the gene. The developmental profile of ribonucleic acid transcribed from one of these regions differs from that of the dopa decarboxylase transcript.

Electron microscopical analysis of Drosophila polytene chromosomes. III. Mapping of puffs developing from one band

Mapping of 16 regions of polytene chromosomes in which 18 one-band puffs develop was carried out with the use of electron microscopy (EM). In most cases a uniform decondensation of the whole band was observed. However, there were examples in which only a part of the band was activated (three puffs) or its right and left parts decondensed simultaneously (three puffs). Splitting of the band into two parts with their further decondensation was also found (one puff). This suggests structural and functional complexity of the bands. On the basis of the data obtained here and those published earlier, a classification of 52 puffs by the number of bands participating in their formation is given. Four classes numbering 22, 21, 7, 2 puffs, developing from 1, 2, 3 and 4 bands, respectively, are revealed. The data show that active chromosome regions are rather diverse in both the pattern of decondensation and expansion of the decondensed region, thus providing evidence of the informational complexity of the majority of active regions.

Isolation and characterization of the dopa decarboxylase gene of Drosophila melanogaster

We have isolated chromosomal deoxyribonucleic acid clones containing the Drosophila dopa decarboxylase gene. We describe an isolation procedure which can be applied to other nonabundantly expressed Drosophila genes. The dopa decarboxylase gene lies within or very near polytene chromosome band 37C1-2. The gene is interrupted by at least one intron, and the primary mode of regulation is pretranslational. At least two additional sequences hybridized by in vivo ribonucleic acid-derived probes are found within a 35-kilobase region surrounding the gene. The developmental profile of ribonucleic acid transcribed from one of these regions differs from that of the dopa decarboxylase transcript.

The genetics of dopa decarboxylase in Drosophila melanogaster. IV. The genetics and cytology of the 37B10-37D1 region

Of 204 mutations located in the 8-12 band Df(2L)130 region, 37B9-C1,2;37D1-2, 199 have been assigned to twelve lethal genes and one visible gene (hook). The 13 genes are not evenly distributed. Twelve, (possibly all thirteen) are in the seven band region 37B10-C4 giving a gene-to-band ratio of almost two. Only one gene, 1(2)37Cf, may be in the four band region 37C5-7, and none are localized in band 37D1. In situ hybridization places the dopa decarboxylase structural gene, Ddc, in or very close to band 37C1,2 (Hirsh and Davidson, 1981). The chi methyl dopa hypersensitive gene, 1(2) and, is 0.002 map units distal to Ddc. Df(2L)VA17, 37C1,2; 37F5-38A1 may actually break in the 37C1,2 singlet. It places six genes, hook, 1(2) and, and four lethal genes, in a maximum of five bands, 37B10, 11, 12, 13 and perhaps part of the 37C1,2 singlet and localizes six genes, Ddc plus five lethal genes, in a maximum of three bands; probably part of the 37C1,2 singlet plus bands, C3, and C4. Wild type activity of five of twelve lethal genes is necessary for female fertility. --Band 37C5 puffs at the time of pupariation; Puff Stages 8-10. Twelve of eighteen alleles of 1(2)37Cf have been examined as heterozygotes over CyO and none affect the appearance of a homozygous 37C5 puff. --Of the 204 mutations considered here only one Ddcpl, affects the function of more than one gene. It eliminates Ddc+ and 1(2)37Ca+ function and at 30 degrees C reduces 1(2)37Ce+ function. It is not a deficiency but could be a polar mutant.

Identification of the Balbiani ring 2 chromomere and determination of the content and compaction of its DNA

The giänt puff Balbiani ring 2 (BR 2) in the salivary glands of Chironomus tentants is known to contain transcriptionally active 75S RNA genes. The corresponding chromosomal superstructure, the BR 2 chromomere, has been identified and characterized in the present study. It was demonstrated by cytological methods that BR 2 originates from the broad band IV-3B10, since all the bands except the 3B10 band could be detected as intact bands in the vicinity of BR 2. In situ hybridization of BR 2 RNA to squashed Malpighian tubule chromosomes lacking BR 2, showed that all or almost all the DNA sequences complementary to BR 2 RNA are located in the 3B10 band. The DNA amount in the 3B10 band, designated the Br 2 band, was measured in relation to the DNA content of the whole chromosome set by both direct and indirect microspectrophotometry of Feulgen-stained Malpighian tubule chromosomes. From a determination of the haploid DNA content in sperm cells (0.25 pg), the amount of DNA in at BR 2 chromomere could then be calculated to be 5.1 x 10-4 pg DNA or 470 kb DNA. A minimum value of the DNA compaction within the BR 2 chromomere was estimated to 380 from the B-form length of BR 2 DNA (160 mum) and the thickness of the BR 2 band (0.42 mum). Since there are only between 1 and 4 75S RNA genes, 37 kb in size, in a BR 2 chromomere, most of the BR 2 DNA must consist of DNA not coding for 75S RNA. The nature of this DNA is discussed in relation to the high average AT-content of Chironomus DNA. The orgnization of the chromosome fiber in the BR 2 chromomere is considered in relation to the gene activation process in the salivary glands, i.e. the formation of a 75S RNA transcription loop from a protion of the tightly packed chromosome fiber in the BR 2 chromomere.