Summary
In order to establish a relationship between the type of genetic alteration occurring in the mutant and the conversion spectrum which is associated with it, an attempt was made to characterize the genetic alterations in a sample of five spore colour mutants by specific reversion.
All the mutants revert by back-mutation. Reversion of one of them is possible by mutation in external suppressor gene: at least two of the external suppressors behave like “super-suppressors”. Reversion of two other mutants by intragenic second-site mutation and study of the intragenic suppressors indicate that they are of the frameshift type. One of the frameshift mutants (ICR170 induced) reverts by two alkylating agents suggesting that it originates from base(s) addition. The inhability of ICR170 to induce reversion of this mutant suggests the preferential occurrence of base addition in ICR170 mutagenesis. Conversly the other frameshift mutant (induced by ethyl methanesulfonate) reverts strongly by ICR170. Thus it is concluded that it originates from deletion.
These two frameshift mutants and all the ICR170 induced mutants give no or very few asci with postmeiotic segregation and either an excess of conversion towards the mutant type allele (addition type mutant) or towards the wild type allele (deletion type mutant).
Evidence supports the hypothesis that mutants which give many asci with postmeiotic segregation originate from substitution.
These data imply differential recognition of “non-pairing” and mispairing of bases and in the case of “non-pairing”, that the direction of conversion is determined by the “non-pairing” itself.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Ames, B. N., Whitfield, H. J.: Frameshift mutagenesis in Salmonella. Cold Spr. Harb. Symp. quant. Biol. 31, 221–225 (1966).
Crick, F. H. C., Barnett, L., Brenner, S., Watts-Tobin, R. J.: General nature of the genetic code for proteins. Nature (Lond.) 192, 1227–1232 (1961).
Drake, J. W.: The molecular basis of mutation, p. 152–156. San Francisco: Holden Day 1970.
Girard, J., Rossignol, J.-L.: In preparation.
Hawthorne, D. C., Mortimer, R. K.: Super-suppressors in yeast. Genetics 48, 617–620 (1963).
Holliday, R.: Mutation and replication in Ustilago maydis. Genet. Res. 3, 472–486 (1962).
Imada, M., Inouye, M., Eda, M., Tsugita, A.: Frameshift mutation in the lysozyme gene of bacteriophage T 4: Demonstration of the insertion of four bases and the preferential occurrence of base addition in acridine mutagenesis. J. molec. Biol. 54, 199–217 (1970).
Kohno, T., Tanemura, S., Yourno, J.: Reversion of the frameshift hisD3018 of Salmonella typhimurium. J. Bact. 102, 655–660 (1970).
Krieg, D. R.: Ethyl methanesulfonate induced reversion of bacteriophage T 4 rII mutants. Genetics 48, 561–580 (1963).
Leblon, G.: Influence de la nature des mutations sur le mécanisme de la conversion génique. Thèse de 3ème cycle. Université Paris-Sud, Centre d'Orsay 1971.
Leblon, G.: Mechanism of gene conversion in Ascobolus immersus. I. Existence of a correlation between the origin of mutants induced by different mutagens and their conversion spectrum. Molec. gen. Genet. 115, 36–48 (1972).
Lissouba, P., Mousseau, J., Rizet, G., Rossignol, J.-L.: Fine structure of genes in Ascobolus immersus. Advanc. Genet. 11, 343–380 (1962).
Malamy, M. H.: Frameshift mutations in the lactose operon of Escherichia coli. Cold Spr. Harb. Symp. quant. Biol. 31, 189–201 (1966).
Malling, H. V.: The mutagenicity of the acridine mustard (ICR170) and structurally related compounds in Neurospora. Mutation Res. 4, 265–274 (1967).
Malling, H. V., Serres, F. J. de: Identification of genetic alterations induced by ethyl methanesulfonate in Neurospora crassa. Mutation Res. 6, 181–193 (1968).
Margolin, P., Bauerle, R. H.: Determinants for regulation and initiation of expression of tryptophan genes. Cold Spr. Harb. Symp. quant. Biol. 31, 311–320 (1966).
Rizet, G., Engelmann, N., Lefort, C., Lissouba, P., Mousseau, J.: Sur un Ascomycète interessant pour l'étude de certains aspects du problème de la structure du gène. C. R. Acad. Sci. (Paris) 270, 2050–2052 (1960).
Rizet, G., Rossignol, J.-L., Lefort, C.: Sur la variété et la spécificité des spectres d'anomalies de ségrégation chez Ascobolus immersus. C. R. Acad. Sci. (Paris) 269, 1427–1430 (1969).
Sarabhai, A., Brenner, S.: A mutant which reinitiates the polypeptide chain after chain termination. J. molec. Biol. 27, 145–162 (1967).
Streisinger, G., Okada, Y., Emrich, J., Newton, J., Tsugita, A., Terzaghi, E., Inouye, M.: Frameshift mutations and the genetic code. Cold Spr. Harb. Symp. quant. Biol. 31, 77–84 (1966).
Whitfield, H. J., Martin, R. G., Ames, B. N.: Classification of aminotransferase (C gene) mutants in the Histidine operon. J. molec. Biol. 21, 335–355 (1966).
Yu-Sun, C.: Nutritional studies of Ascobolus immersus. Amer. J. Bot. 51, 231–237 (1964).
Author information
Authors and Affiliations
Additional information
Communicated by W. Gajewski
Rights and permissions
About this article
Cite this article
Leblon, G. Mechanism of gene conversion in Ascobolus immersus . Molec. Gen. Genet. 116, 322–335 (1972). https://doi.org/10.1007/BF00270089
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF00270089