Worm Breeder's Gazette 10(1): 56

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

A Pseudogene, hsp70B, of the Heat Shock Inducible hsp70A Gene

M.F.P. Heschl and D.L. Baillie

In the ongoing saga of the hsp70 multigene family, we have recently 
sequenced the hsp70B gene.  It has been suggested that the hsp70B gene 
is a pseudogene of the constitutively expressed, heat inducible hsp70A 
gene (Snutch, Heschl and Baillie, manuscript submitted).  This was 
based on the ability of the hsp70B gene to cross-hybridize with the 
hsp70A gene under conditions of high stringency.
Sequence analysis of the hsp70B gene and a comparison to the hsp70A 
gene show 
1) the homology starts within the 5' untranslated leader sequence 
but does not include the 5' regulatory region,
2) only two of the introns and their positions are conserved,
3) the hsp70B sequence lacks the last 40% of the corresponding 
hsp70A sequence including the last intron,
4) there are two stop codons within the hsp70 reading frame,
5) there are several single base pair deletions and one insertion 
resulting in frameshifts.  The one insertion is compensated for by a 
deletion 3 bp downstream,
6) there is an internal deletion of 243 bp,
7) the nucleotide substitution rate at the third, second and first 
codon positions are 12.1%, 5.2% and 7.2% respectively, 
8) there is a greater number of deletions and insertions occurring 
within the introns than within the 'coding region' of hsp70B.
Features #3 to #6 support the idea that the hsp70B gene is a 
pseudogene of hsp70A.  Features #7 and #8 suggest that the hsp70B gene 
was functional for a while after the hsp70A gene duplication event (
third codon position substitution rate is almost double that of the 
first and second positions.  If the gene was inactive from the point 
of the duplication event, the number and types of mutations would have 
been the same regardless of the codon position or position within the 
intron or the coding region.)  We are currently attempting to 
calculate when the hsp70A gene was duplicated.  A putative TATA box 
was found in a position similar to that of the hsp70A gene although 
the surrounding nucleotide sequence is very different.  In addition, 
there are two possible poly A addition sites (with one base pair 
differences) downstream of the hsp70B/hsp70A homology.
It will be interesting to see if this pseudogene, which is not 
present in the sister species C.  briggseae, is present in any, or all,
of the other wildtype strains of C.  elegans.  This information could 
tell us when the different wildtype strains diverged.