Characterization of Mutations Affecting the Escherichia Coli Essential Gtpase Era That Suppress Two Temperature-Sensitive Dnag Alleles

Author:

Britton, R. A.

Powell, B. S.

Court, D. L.

Lupski, J. R.
Author Address

Lupski JR BAYLOR COLL MED DEPT MOL & HUMAN GENET HOUSTON, TX 77030 USA BAYLOR COLL MED DEPT MOL & HUMAN GENET HOUSTON, TX 77030 USA BAYLOR COLL MED CELL & MOL BIOL PROGRAM HOUSTON, TX 77030 USA BAYLOR COLL MED DEPT PEDIAT HOUSTON, TX 77030 USA NCI GENE REGULAT & CHROMOSOME BIOL LAB ABL BASIC RES PROGRAM FREDERICK CANC RES & DEV CTR FREDERICK, MD 21702 USA

Abstract:

Two suppressor mutations of the temperature-sensitive DNA primase mutant dnaG2903 have been characterized. The gene responsible for suppression, era, encodes an essential GTPase of Escherichia coli. One mutation, rnc-15, is an insertion of an IS1 element within the leader region of the rnc operon and causes a polar defect on the downstream genes of the operon. A previously described polar mutation, rnc-40, was also able to suppress dnaG2903. The other mutation, era-1, causes a single amino acid substitution (P17R) in the G1 region of the GTP-binding domain of Era. Analysis of the GTPase activity of the Era-1 mutant protein showed a four- to five-fold decrease in the ability to convert GTP to GDP. Thus, lowered expression of wild-type Era caused by the polar mutations and reduced GTPase activity caused by the era-1 mutation suppresses dnaG2903 as well as a second dnaG allele, parB. Phenotypic analysis of the era-1 mutant at 25 degrees C showed that 10% of the cells contain four segregated nucleoids, indicative of a delay in cell division. Possible mechanisms of suppression of dnaG and roles for Era are discussed. [References: 34]

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