Interacting genes that affect microtubule function: the nc2 allele of the haywire locus fails to complement mutations in the testis-specific beta-tubulin gene of Drosophila.

Abstract

A mutation that fails to complement certain alleles of the testis-specific [32-tubulin gene (B2t) of Drosophila melanogaster maps to a separate locus, haywire, located at 3-34.4 map units in polytene region 67E3-F3. Second-site non-complementing mutations such as hay ~c2 and B2t alleles could identify genes that encode products that participate in the same functions or that interact in the same structure. Consistent with a structural interaction between the hay gene product and [32-tubulin, the genetic interaction between hay ~2 and B2t requires the presence of the mutant hay gene product; a deficiency for the hay region complements the same alleles of B2t that hay ~2 fails to complement, hay n~2 is a recessive male sterile mutation in a genetic background that is wild type at the B2t locus. Homozygous males have defects in meiosis, flagellar elongation and nuclear shaping, the three major microtubule-based processes in which the testis-specific [32-tubulin participates. The hay ~z allele also has effects outside of spermatogenesis. It is a temperature-sensitive semilethal mutation, and homozygous hay ~2 females have reduced fertility. These phenotypes are consistent with a role for the haywire gene product in general microtubule function. Analysis of second-site noncomplementing mutations such as hay ~2 offers a genetic tool for analysis of interacting proteins in complex assemblies.

Interacting proteins identified by genetic interactions: a missense mutation in alpha-tubulin fails to complement alleles of the testis-specific beta-tubulin gene of Drosophila melanogaster.

“…Recessive mutations that fail to complement P2-tubulin alleles but do not map to any known a-or P-tubulin genes have been isolated (9,46,47). If the genetic interaction between these mutations and B2t is based on structural interactions between the gene products, as shown for nc33, then the loci identified by these mutations are good candidates for genes encoding MAPs or other structural components of complex microtubule arrays.…”

“…Screens for new alleles of the B2t gene identified mutations that failed to complement recessive alleles of B2t but did not map to the B2t locus (9,46,47). One of these second-site noncomplementing mutations, nc33, was closely linked to the ax-tubulin gene in polytene interval 84B (9 amino acid substitution in the ot-tubulin protein encoded by tubA84B, and we discuss a possible mechanism for the failure to complement between mutations in genes encoding a-and P-tubulin.…”

Hfp inhibitsDrosophila myctranscription and cell growth in a TFIIH/Hay-dependent manner

“…TFIIH is a multi-protein complex, but in vitro studies suggest that the active subunit in Pol II escape and transcriptional control of cmyc is the DNA helicase XPB (Liu et al, 2001;Liu et al, 2000;. Haywire (Hay) is the Drosophila orthologue of the mammalian XPB helicase (Merino et al, 2002;Mounkes and Fuller, 1999;Mounkes et al, 1992;Regan and Fuller, 1988).…”

Defective Hfp-dependent transcriptional repression of dMYC is fundamental to tissue overgrowth in Drosophila XPB models

“…The conserved domains between the Human-XPB and Drosophila-Hay protein are highlighted and include the N-terminal DNA binding domain, several helicase domains and the C-terminal domain. The Drosophila Hay nc2 allele was first identified in 1988 45,54 and characterized as a point mutation at amino-acid position 652 in the sixth helicase domain 18,40,50,51,54 . Subsequently, following ethyl methane sulfonate-induced mutagenesis, several other Hay mutants were generated in the Hay nc2 background and molecularly characterized 41,54 .…”

“…XPB regulates post-initiation control of MYC transcription via the RNA recognition motif protein FIR and the KH domain protein FBP 16,23,24,45 . Specifically, under the conditions of activated (serum stimulated) MYC transcription, XPB is required for recruiting both FBP and FIR to a single-stranded promoter sequence (the far upstream sequence element) 1.7 kB upstream of the MYC TSS 16,23,40 .…”