Subject: Re: Structure of the 87C1 locus of D. melanogaster
Hello!
I have also been contacted by Wei Gong in K. Golic's lab regarding the 87C1
area and confusion over copy number. As far as I can tell, the y; cn bw sp
chromosome which was sequenced in the Drosophila genome project has three,
not two, tandemly repeated hsp70 genes at 87C1. If you look at BACR02G11,
there \*is* a reverse-orientation hsp70 gene, hsp70Ba, near the beginning of
the BAC. About 40kb downstream are the three tandemly-repeated
copies. This arrangement, which I've never observed on any natural
chromosomes in small-scale analyses, has been reported on the Cu Kar Sb
balancer, and also in a Drosophila cell line. Detecting the 'extra' copy
on natural chromosomes via Southern blotting or similar techniques would be
very difficult given the extreme similarity of the two innermost tandem
copies,
and as such an exhaustive analysis has not been conducted. Thus, I can not
speculate on the actual frequency of this gene arrangement in natural
populations.
If you can indeed verify that there the three hsp70s in tandem on
BACR02G11, the problem will become one of nomenclature. The distalmost
copy is definitely hsp70Bc, as it retains the divergent 3'-UTR. So what to
call the other two tandem hsp70s, if the name hsp70Ba is reserved for the
reverse-orientation copy? Given that the inner two tandem copies are
virtually identical, I would propose hsp70Bb and hsp70Bb-prime or something
similar. The original hsp70 nomenclature was proposed by Leigh Brown and
Ish-Horowicz in 1981-
Leigh Brown AJ, Ish-Horowicz D.
Evolution of the 87A and 87C heat-shock loci in Drosophila.
Nature. 1981 Apr 23;290(5808):677-82.