János Gausz

A new homeotic mutation in the Drosophila bithorax complex removes a boundary separating two domains of regulation

The bithorax complex specifies the identity of parasegments 5‐14 of Drosophila. Although nine parasegment‐specific functions, abx/bx, bxd/pbx and iab‐2 to iab‐8,9 have been identified, the whole bithorax complex appears to encode only three classes of proteins, Ubx, abd‐A and Abd‐B. Many observations suggest that the parasegment‐specific functions act as positive cis‐regulatory elements of Ubx, abd‐A and Abd‐B. We report the molecular genetics of a new gain‐of‐function mutation, Fab‐7, which transforms parasegment 11 into parasegment 12. Induction of Abd‐B mutations in cis (one of which removes the Abd‐B homeobox) causes reversion of the dominant phenotype, demonstrating that Fab‐7 misregulates Abd‐B. A 4 kb deletion, 30 kb downstream from the Abd‐B transcription unit, is solely responsible for the Fab‐7 phenotype. We consider that the parasegment‐specific functions lie in DNA domains that are sequentially and independently ‘opened’ along the chromosome. Once a domain is opened, the cis‐regulatory sequences within it can carry out their function. We propose that the Fab‐7 deletion removes a boundary separating the iab‐6 and iab‐7 cis‐regulatory regions (the functions specific for parasegments 11 and 12) allowing the open configuration of iab‐6 to invade iab‐7 in parasegment 11. This is strongly supported by our finding that Fab‐7 can be caused to revert by lesions not only in iab‐7 but also in iab‐6.

Modifiers of position-effect variegation in the region from 86C to 88B of the Drosophila melanogaster third chromosome

SummaryFour dominant suppressor and one enhancer of variegation loci were mapped in the polytene chromosome region extending from section 86C to section 88B of the Drosophila melanogaster third chromosome using a set of deficiencies. The suppressor locus Su-var(3) 14 maps in 86CD, Su-var(3) 13 in 86F4-7, Su-var(3)6 in 87B4-7 and Su-var(3)7 in 87E4-5. The enhancer locus E-var(3)3 maps in 87E12-F11. Su-var(3)13, Su-var(3)6 and Su-var(3)7 are also defined by point mutant alleles originally identified by other criteria (Reuter et al. 1986). Duplications covering the suppressor loci Su-var(3)14, Su-var(3)13, Su-var(3)6 and Su-var(3)7 were found to reduce considerably the haplo-abnormal effect of heterozygous point mutants of the corresponding loci. One suppressor locus, Su-var(3)7, maps within a region which has previously been cloned. The positions of deficiency breakpoints delimiting the suppressor locus indicate that all the necessary sequences for its function are located within 10 kb of cloned DNA.

Deletion mapping of two D. melanogaster loci that code for the 70,000 dalton heat-induced protein

Using deficiencies in D. melanogaster that lack either the 87A or 87C heat-induced puffs, we have shown that the 70,000 dalton heat-induced protein (hsp 70) is encoded at both these loci. Embryos deleted for one of the two loci retain the ability to make hsp 70 after heat shock, but deleting both loci eliminates synthesis of hsp 70. Thus both loci encode hsp 70 and can be active following heat shock. We have analyzed the proteins made by embryos lacking either 87A or 87C, and have compared the 87A- and 87C-coded hsp 70 by isoelectric focusing and tryptic peptide fingerprinting. The hsp 70 made by the two loci is very similar, although a variant tryptic peptide appears to be encoded only at 87C. Using deficiencies with slightly different breakpoints, we have mapped the 87A locus to band 87A7, the site of the 87A heat-induced puff. The 87C locus maps within 87C1.

Tissue specific expression of the acetylcholinesterase gene in Drosophila melanogaster

SummaryAcetylcholinesterase activity is present in both particulate and soluble forms in wild-type Drosophila melanogaster embryos. The particulate form of the enzyme is localized in the CNS, while the soluble forms are non-CNS-specific. Deletion mapping studies show that all AChE activity is abolished if the cytological region between 87E1-2 and 87E4 is missing. An additional region mapping to the proximal part of the 87E4 band is needed for CNS-specific AChE activity

Genomic organization and functional analysis of a deletion variant of the 87A7 heat shock locus of Drosophila melanogaster.

The major 70,000 Mr heat-induced protein (hsp 70) of Drosophila melanogaster is encoded at two loci, 87A7 and 87C1. The 87A7 locus has two hsp 70-coding sequences (zc) about 2·8 × 103 bases apart in a divergent orientation. We have identified a variant 87A7 locus, the Sze-13 chromosome, which has a reduced heat shock puff. Characterization of this altered 87A7 locus reveals that it has a small deletion in the spacer between the two genes that inactivates the proximal gene. The mutant locus has been cloned and the breakpoints of the deletion determined by sequence analysis. We find that the deletion removes the entire 5′ half of the proximal hsp 70 gene and extends to position −479 base-pairs upstream from the start of transcription of the distal gene. Using flies that retain only the mutant 87A7 hsp 70 locus of Sze-13 we have shown that the one remaining “intact” hsp 70 gene is still active. Since a partially deleted hsp 70 gene lacking the 3′ half of the transcription unit is also active, it is likely that the initial portion of the transcription unit (zc) plus the conserved znc sequence that is immediately adjacent to the 5′ end of the gene contain the sequences necessary for hsp 70 expression.

Genetic and cytogenetic studies of malic enzyme in Drosophila melanogaster

The genetic and cytogenetic locations of the structural gene (Men) for malic enzyme have been determined. Men maps genetically between kar and ry at 51.73±0.02. Cytogenetically, Men probably lies in the proximal edge of 87D1,2, based on the results of mapping utilizing a number of deficiencies with breakpoints in that region. A number of null alleles have been recovered; heterozygotes for these nulls and a Men deficiency are both viable and fertile. These findings are related to the one band, one functional unit model of salivary gland chromosome structure.