Characteristics of gene conversion and Rec factor of the i locus of Sordaria fimicola.

Abstract

Apart from the previously studied g-locus, the i-locus showed the following characteristics.I. One-point cross conversion frequencies were roughly constant around 10 x 10-3, unless associated with a Rec+ factor. II. The interallelic conversion frequencies were either the sum of parental one-point cross conversion frequencies (20 X 10-3) or still higher than this, suggesting that this locus has compound composition with at least two units. III. Whenever interallelic cross conversion frequency was notably higher than 20 x 10-3, the ascus frequency of the spore colour ratio, 2+, 2i, 4b (asci of this composition can be developed through gene conversion or appear as tetratypes through reciprocal recombination) was high enough to include the excess portion of the conversion frequency, leaving substantial surplus. This suggests that the i-locus is composed of multiple units, and at the joints of units ordinary reciprocal cross-overs occur producing tetratype asci; and cosequently raising the apparent conversion frequencies. IV. The original blur allele was accompanied with a Rec+ factor, and therefore, its conversion frequency was low. Through gene conversion, this factor was removed from bins and transferred to the wild type allele. V. The Rec factor functions as a mutator on the alleles in the i-locus, and by itself, it was labile. Among the above characteristics, III and V respectively show close relationships with the compound genes of Neurospora and the mutable genes of Zea.

Composition of eukaryotic gene loci regarding gene conversion units and the presence or the absence of intralocus reciprocal recombination.

“…Recent reports on the separate occurrence of reciprocal recombination from gene conversion events (Roman and Fabre, 1983;Klein, 1984;Willis and Klein, 1987;Bollag and Liskey, 1988) support the previous finding by Kitani (1982), and provide a favorable atomosphere of expressing the fact. The fact is that there are two kinds of loci in Sordaria fimicola; one in which reciprocal recombination does not occur, and the other in which it occurs.…”

“…On the contrary, the indigo ascospore locus (i-locus) of S. fimicola was, however, appeared to undergo intralocus reciprocal recombination, and showed various conversion frequencies in interallelic crosses (Kitani, 1982).…”

“…Various data from the g-locus analysis suggest that gene conversion and conversion-associated flanking marker exchanges are the phenomena arising from an integrated mechanism (Kitani and Olive, 1967, 1970, Kitani, 1978a, 1978b, 1982. And the data from the i-locus analysis suggest that intralocus reciprocal recombination occurs by a separate mechanism from the one for gene conversion and its associated flanking marker exchanges (Kitani, 1982).…”

“…And the data from the i-locus analysis suggest that intralocus reciprocal recombination occurs by a separate mechanism from the one for gene conversion and its associated flanking marker exchanges (Kitani, 1982). Thus, having two types of locus in a single organism, one with and the other without the ability of intralocus reciprocal recombination, one may expect to determine the DNA structure (base sequence) responsible for the reciprocal recombination, if the complete nucleotide sequences for the loci g and i are determined and compared with each other.…”

Tests of double-strand gap repair as a major source of meiotic gene conversion in fungi

“…Closelylinked sites within a locus generally have very similar basic frequencies of conversion events (Paquette and Rossignol, 1978;Kitani and Whitehouse, 1974;Kitani, 1982), which could either result from very similar frequencies of hDNA or from being included in gap repair regions with very similar frequencies, or from equal frequencies of some mixture of the two types of event. This is consistent with current ideas of initiation of recombination on either gap repair or hDNA models, with initiation events giving gaps or hDNA lengths over a series of sites.…”