C. Grimm et al., M26 RECOMBINATIONAL HOTSPOT AND PHYSICAL CONVERSION TRACT ANALYSIS INTHE ADE6 GENE OF SCHIZOSACCHAROMYCES-POMBE, Genetics, 136(1), 1994, pp. 41-51
At the ade6 locus of Schizosaccharomyces pombe flanking markers have b
een introduced as well as five silent restriction site polymorphisms:
four in the 5' upstream region and one in the middle of the gene. The
mutations ade6-706, ade6-M26 (both at the 5' end) and ade6-51 (middle
of the gene) were used as partners for crosses with the 3' mutation ad
e6-469. From these three types of crosses, wild-type recombinants were
selected and analyzed genetically to assess association with crossing
-over and physically to determine conversion tract lengths. The introd
uced restriction site polymorphisms (five vs. only one) neither influe
nced the pattern of recombinant types nor the distribution of conversi
on tracts. The hotspot mutation M26 enhances crossing-over and convers
ion to the same proportion. M26 not only stimulates conversion at the
5' end, but does this also (to a lower extent) at the 3' end of ade6 a
t a distance of more than 1 kb. The majority of meiotic conversion tra
cts are continuous and postmeiotic segregation of polymorphic sites is
rare. Conversion tracts are slightly shorter with M26 in comparison w
ith its control 706. The mean minimal length of tracts varies from 670
bp (M26) to 890 bp (706) to 1290 bp (51). It is concluded that M26 ac
ts as an initiation site of recombination or enhances initiation of re
combination. M26 does not act by termination of conversion. A region o
f recombination initiation exists at the 5' end of the ade6 gene also
in the absence of the ade6-M26 hotspot mutation.