Decapentaplegic: a gene complex affecting morphogenesis in Drosophila melanogaster

The decapentaplegic gene complex (2-4.0) in Drosophila melanogaster is defined by a series of allelic mutations affecting imaginal disk development. Decapentaplegic (dpp) mutant individuals exhibit a variety of pattern deficiencies and duplications in structures derived from one or more of the 15 major imaginal disks. Based on dpp mutant phenotypes, we suggest that the dpp gene complex is involved in the elaboration of positional information within developing epidermal tissue. The dpp mutations are recessive and fall into six phenotypic classes. Milder alleles (classes I and II) affect only one or a few disks while most alleles (classes III, IV, V and EL) affect all major imaginal disks. Class EL homozygotes are embryonic lethals; development is arrested before germ-band shortening late in gastrulation. Presently inseparable from EL, is a haplo-insufficient function (Hin-d) associated with the distal (left) end of the dpp gene complex. The dpp gene complex occupies most or all of 22F1--3, three densely staining polytene chromosome bands. A colinearity exists between map positions of the four identified functional units within the complex and the severities of mutant phenotypes caused by disruption of these functions. Most dpp mutations are gross chromosomal rearrangements; they exert polar effects on the decapentaplegic functions that are proximal to the rearrangement breakpoints in 22F. Many structural similarities exist between the decapentaplegic and bithorax gene complexes.     

The gene specifying RNase E (rne) and a gene affecting mRNA stability (ams) are the same gene

A DNA clone complementing the rne-3071 mutation has been expressed and localized in the physical map of Escherichia coli. The DNA fragment from this clone was localized to the region of the E. coli chromosome where the rne-3071 mutation has been mapped. The position of this DNA fragment in the E. coli chromosome, the size of the product directed by this DNA fragment (110,000 Da), the restriction map of this fragment, the fact that the same clone complements the ams mutation, and the observation that the rne-3071 and the ams mutations cause similar patterns of RNA synthesis, show that the rne gene--a gene specifying the processing endonuclease RNase E--and the ams gene--a gene that affects mRNA stability--are identical.     

Mercury(II) binding to s4U in E. coli tRNA(Val)

The accessibility of the s⁴U base in native tRNA^Val from E.coli was monitored by studying the binding of various mercurials. The relative binding order HgBr₂[unk]HgCl₂CH₃HgOAc[unk]CH₃HgCl[unk]PCMB parallels approximately the steric requirements of linear HgX₂ or RHgX compounds for S_N2 displacement by sulfur, although other factors are operative. Para-chloromercuri-benzoate (PCMB) does not bind the thiolated nucleotide unless the tertiary structure of the tRNA is opened up by removal of Mg²⁺ ions and heating to 40°. Under these conditions, equilibrium dialysis measurements using ¹⁴C-labeled PCMB showed one binding site (n = 0.93) with an association constant, K₁, of 9 × 10⁴M⁻¹.     

Modulation of transcription factor activity by a distant steroid modulatory element.

Variations in the biological activity of antisteroids, as determined by their percent agonist activity, is a well known but poorly understood phenomenon. For example, in tyrosine aminotransferase (TAT) induction by the antiglucocorticoid dexamethasone 21-mesylate in rat hepatoma tissue culture cells, the percent agonist activity varies with the density of cultured cells. A 21-basepair sequence of the rat TAT gene has now been isolated which confers all of the induction properties of the endogenous TAT gene to homologous and heterologous promoters and genes. We call this 21-basepair sequence, which acts in concert with a trans-acting factor identified by gel shift experiments, a glucocorticoid modulatory element. The changes in induction properties were found to be independent of the fold induction by dexamethasone, thus arguing that the GME does not synergize with the glucocorticoid response element. A model incorporating this new element is advanced which can explain the observed variations of TAT induction and may be generally applicable for the mechanism of action of other steroid hormones.     

tRNA derived insertion element in histone gene repeating unit of Drosophila melanogaster.

Analysis of 41 histone homologous clones from an isogenic gene library of Drosophila melanogaster showed that non-histone fragments interrupt the histone repetitive clusters at several sites. Long (L) and short (S) forms of the repeating units are distinguished by the insertion of 240 bp into the spacer between H1 and H3 of the L units; Each form appears to be clustered with its own kind. The complete DNA sequence of the histone 5.0 kb repeating unit was determined. Five histone genes (H1, H2A, H2B, H3, H4) were identified in a repeating unit and several sequence blocks common to the five histone genes were found in the 5'- and 3'-regions. The insertion sequence of 240 bp was found to be similar to the Alu family, an element derived from tRNA.     

A tRNA Val(GAC) gene of chloroplast origin in sunflower mitochondria is not transcribed

A tRNA^Val (GAC) gene is located in opposite orientation 552 nucleotides (nt) down-stream of the cytochrome oxidase subunit III (coxIII) gene in sunflower mitochondria. The comparison with the homologous chloroplast DNA revealed that the tRNA^Val gene is part of a 417 nucleotides DNA insertion of chloroplast origin in the mitochondrial genome. No tRNA^Val is encoded in monocot mitochondrial DNA (mtDNA), whereas two tRNA^Val species are coded for by potato mtDNA. The mitochondrial genomes of different plant species thus seem to encode unique sets of tRNAs and must thus be competent in importing the missing differing sets of tRNAs.