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J. Bacteriol., 08 1995, 4402-4409, Vol 177, No. 15
P Fajardo-Cavazos and WL Nicholson
In response to UV irradiation, Bacillus subtilis spore DNA accumulates the
unique thymine dimer 5-thyminyl-5,6-dihydrothymine, or spore photoproduct
(SP). SP is broken down into monomers during spore germination by the
product of the spl gene which has been proposed to encode the enzyme SP
lyase. The wild-type spl gene was cloned by complementation of a mutation
designated spl-1; the putative spl gene product is a 40-kDa protein whose
deduced amino acid sequence contains regions homologous to DNA photolyases.
During phenotypic characterization of spl subclones using transformation
crosses between the cloned wild-type spl gene and an spl-1 mutant
recipient, in addition to the expected transformant classes exhibiting
UV-resistant (type I) and UV-sensitive (type III) spores, an additional
recombinant class was observed (called type II), spores of which exhibited
slower germination kinetics following UV irradiation. The results suggested
that the spl-1 allele consisted of at least two separable mutations. The
DNA region which could rescue the spl-1 allele was localized to a 511-bp
region within the spl coding sequence; this region was amplified from the
spl-1 mutant chromosome by PCR and sequenced. The region contained two
amino acid substitutions, an Arg replacing Gly-168 (G168R) and an Asp
replacing Gly-242 (G242D) in the deduced SP lyase sequence, as well as 18
silent mutations.(ABSTRACT TRUNCATED AT 250 WORDS)
Copyright © 1995, American Society for Microbiology
Molecular dissection of mutations in the Bacillus subtilis spore photoproduct lyase gene which affect repair of spore DNA damage caused by UV radiation
Department of Microbiology and Immunology, University of North Texas Health Science Center, Fort Worth 76107, USA.
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