The Role of Recombination in Growth of Bacteriophage Lambda I. The Gamma Gene

Abstract

Although recombination in microorganisms has been studied extensively, the role of recombination in growth is not entirely understood. For example, it is not yet clear to what extent recombination proteins are involved in events such as repair or synthesis of DNA.

One way to approach the problem is to study the effect on growth of a deficiency in recombination. Recombination-deficient mutants have been isolated in several systems. In E. coli (Howard-Flanders and Theriot, 1966; Clark, 1967) they define three cistrons recA, B, and C, of which B and C determine an exonuclease (Barbour and Clark, 1970). None of the three cistrons appears to be essential for cell growth, since the mutants are viable. (However, since the selection procedure scored only viable cells, these mutants might retain a low but essential level of the gene products.)

Recombination-deficient mutants have also been isolated in several bacteriophages. In phage P22, these mutants (erf⁻) grow in rec⁺ but not in rec⁻ hosts, suggesting that recombination proteins are essential for growth in P22 (Botstein and Matz, 1970). In phage T4, mutations in several essential cistrons seem to affect recombination (Bernstein, 1968).

In phage λ, recombination-deficient mutants (red⁻, Signer and Weil, 1968; Echols and Gingery, 1968) define two genes (Shulman et al., 1970), namely exo (exonuclease, Korn and Weissbach, 1963) and β (beta protein, Radding and Schreffler, 1966). In this phage neither gene appears to be essential for growth, since both exo⁻ mutants (including deletion mutants) and β⁻ mutants (including amber mutants) make plaques on rec⁻...