Escherichia coli DNA glycosylase Mug: a growth-regulated enzyme required for mutation avoidance in stationary-phase cells

Mokkapati, SK de Henestrosa, ARF Bhagwat, AS

Sk. Mokkapati et al., Escherichia coli DNA glycosylase Mug: a growth-regulated enzyme required for mutation avoidance in stationary-phase cells, MOL MICROB, 41(5), 2001, pp. 1101-1111

45

INGLESE

Article

Microbiology

MOLECULAR MICROBIOLOGY

0950-382X → ACNP

41

5

2001

1101 - 1111

ISI

0950-382X(200109)41:5<1101:ECDGMA>2.0.ZU;2-1

The Escherichia coli DNA glycosylase Mug excises 3,N-4-ethenocytosines (eps ilonC) and uracils from DNA, but its biological function is obscure. This i s because epsilonC is not found in E. coli DNA, and uracil-DNA glycosylase (Ung), a distinct enzyme, is much more efficient at removing uracils from D NA than Mug. We find that Mug is overexpressed as cells enter stationary ph ase, and it is maintained at a fairly high level in resting cells. This is true of cells grown in rich or minimal media, and the principal regulation of mug is at the level of mRNA. Although the expression of mug is strongly dependent on the stationary-phase sigma factor, sigma (S), when cells are g rown in minimal media, it shows only a modest dependence on sigma (S) when cells are grown in rich media. When mug cells are maintained in stationary phase for several days, they acquire many more mutations than their mug(+) counterparts. This is true in ung as well as ung(+) cells, and a majority o f new mutations may not be C to T. Our results show that the biological rol e of Mug parallels its expression in cells. It is expressed poorly in expon entially growing cells and has no apparent role in mutation avoidance in th ese cells. In contrast, Mug is fairly abundant in stationary-phase cells an d has an important anti-mutator role at this stage of cell growth. Thus, Mu g joins a very small coterie of DNA repair enzymes whose principal function is to avoid mutations in stationary-phase cells.