Induction by RNA of inositol independence in Neurospora crassa.

Abstract

Contributed by E. L. Tatum, December 9, 1974 -ABSTRACTThe effect of purified wild-type RNA (allo-RNA) on genetic reversion of inositol-requiring mutant 89601 of Neurospora crassa is described. The mutant (inos-) strain, on treatment with the wild-type RNA preparation, was found to revert to wild type (inos+) in significant numbers. RNA from the mutant (iso-RNA) and allo-RNA digested by RNase were ineffective in causing genetic reversion at the inositol locus. The allo-RNA-induced revertants were stable and showed a Mendelian transmission of the inos+ character.The role of DNA in genetic transformation is well known (1). Recently, such a role for RNA has been suggested by work with several biological systems. The acquisition of a drugresistant character by sensitive bacteria after treatment with purified RNA preparations from resistant strains has been described in pneumococcus (2), Bacillus subtilis (3), and Escherichia coli (4). The transfer of other genetic characters mediated by purified RNA preparations has also been reported (5, 6). In higher organisms the development of specifictissues in response to exogenous RNA during organ culture has been described (7,8). The possible role of RNA in transfer of genetic information is supported by the discovery of the enzyme, reverse transcriptase (RNA-dependent DNA polymerase) (9, 10), which can transcribe an RNA template into DNA. In this paper we describe the effect of exogenous RNA on genetic reversion at the inositol locus of Neurospora crassa. A preliminary account of this work has been presented (11).MATERIALS AND METHODSStrains. The Neurospora strains used were the wild-type (RL3-8A, RL21a) strains, the inositol-requiring morphological mutant strain (R2506-8-12, inos-rg-A) and the inositolrequiring strain 89601. These strains were obtained from the Rockefeller University collection and were maintained on minimal medium (12) supplemented with inositol.Chemicals. Deoxyribonuclease I (RNase-free) and ribonuclease were obtained from Worthington Biochemical Co. Other chemicals were reagent grade. Nitrocellulose membranes were obtained from the Millipore Co.Genetic Analysis. The genetic crosses were made on synthetic crossing medium (13). The genetic crosses and the heterokaryon analysis were performed by standard methods as described earlier (14). A large sample of ascospores was analyzed by methods described by Giles (15).Equal aliquots of ascospore suspension were added to liquified agar sorbose medium (16) with or without inositol supplement. After a heat treatment at 600 for 30 min, the medium containing the ascospores was distributed in sterile disposable petri plates (25 ml per plate). These plates were incubated at 250 for about 70 hr and then the growing colonies were counted.The inositol-independent revertant strains were examined for heterokaryosis (inos+/inos-) by plating equal aliquots of a suspension of conidia or mycelial fragments on sorbose-agar medium with and without inositol supplement. For a heterokaryotic culture, the number of colonies growi...

Variations dans ľexpression du pouvoir oncogène d'Agrobacterium tumefaciens

“…Agrobacterium tumefadens) y provoque des bouleversements d'ordre biochimique et physiologique. Une "transformation genetique" par l'intermediaire d'un ARN a ete egalement trouvee dans d'autres systemes biologiques (Mishra et al 1975). Cependant, le caractere temporaire des variations dans l'expression du pouvoir tumorigene des bacteries tel que nous l'avons etudie s'accorde mal, en apparence du moins, avec la permanence qui caracterise un phenomene genetique.…”