Tuesday, November 27, 2007

Hsp70: Mycoplasma vs. Mimivirus

I'm still trying to get over the fact that one percent of the genome of Mycoplasma genitalium (an organism with an extremely stripped-down genome) is devoted to genes for heat-shock proteins. (See earlier blog.) This is a prokaryote with a genome smaller than that of many viruses (just 580K base pairs).

For fun, I decided to do a BLAST-n search to see if the dnaK gene of M. genitalium has any homologs in the virus world. My search scored a weak hit (61.9 bits) on a gene in Acanthamoeba polyphaga mimivirus. The (enormous) 1.2Mbp mimivirus genome is known to encode for a heat-shock protein of the Hsp70 type. That's where my hit was.

I followed up with a protein (BLAST-p) comparison of the M. genitalium dnaK gene product against the mimivirus Hsp70 protein, which confirmed the match (452 bits; identities = 255/606; positives = 370/606).

So not only does the smallest known prokaryotic organism have an Hsp70 gene, but the largest known virus has one as well.

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