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Two locally acting genetic controls of gene conversion, ccf-5 and ccf-6, in Ascobolus immersus

Published online by Cambridge University Press:  14 April 2009

W. M. Howell  and
B. C. Lamb
W. M. Howell
Affiliation:
Department of Pure and Applied Biology, Imperial College, London SW7 2BB
B. C. Lamb
Affiliation:
Department of Pure and Applied Biology, Imperial College, London SW7 2BB
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Two new conversion control factors (ccfs), ccf-5 and ccf-6, have been characterized in the Pasadena strains of Ascobolus immersus. Both are monogenic, with two known allelic forms (called A and B) of each factor, and affect the frequency of meiotic gene conversion at a white (w) ascospore locus closely linked to it, ccf-5 affecting w-9 and ccf-6 affecting w-BHj. The ccfs appear to be specific to their own target site, with no effect on at least nine unlinked w mutations. Conversion of the w locus affected was studied in + × w crosses with all four possible ccf arrangements: for example, for + × w-9, with ccf-5(A) in both parents, with ccf-5(B) in both parents, with ccf-5(A) in +, B in w-9, and with ccf-5(B) in +, A in w-9. For both ccfs, there were slight differences between crosses homozygous for A and those homozygous for B, and also slight differences between the two forms of heterozygous cross, A/B and B/A, but the major effect was for heterozygosity for the control factor to depress conversion frequency of the w locus, compared with either homozygous state. These two ccfs are compared with other sites affecting recombination in fungi and higher eukaryotes. Two possible modes of action of ccfs 5 and 6 are (i) on pairing closeness before hybrid DNA initiation, and (ii) on later stages such as the spread of hybrid DNA from an initiation point.

Type
Research Article
Information
Genetics Research , Volume 43 , Issue 2 , April 1984 , pp. 107 - 121
Copyright
Copyright © Cambridge University Press 1984

References

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