Transport of Vitamin B12 in Escherichia coli: Genetic Studies

AUTOR(ES)
RESUMO

The chromosomal location of two genetic loci involved in the transport of cyanocobalamin (B12) in Escherichia coli K-12 was determined. One gene, btuA, is believed to code for the transport protein in the cytoplasmic membrane, because a mutant with an alteration in this gene has lost the ability to accumulate B12 within the cell although normal levels of the surface receptors for B12 are present. The other locus, btuB, apparently codes for the surface receptor on the outer membrane. These mutants have lost the ability to bind B12 and have greatly reduced transport activity, although growth experiments have shown that they can utilize B12 for growth, but with decreased efficiency. This surface receptor for B12 also appears to function as the receptor for the E colicins, because btuB mutants are resistant to the E colicins, and mutants selected for resistance to colicin E1 are defective in B12 binding and transport. The gene order was determined by transduction analysis to be cyc-argH-btuA-btuB-rif-purD. In addition, mutations in metH, the gene for the B12-dependent homocysteine methylating enzyme, were obtained in this study. This gene was localized between metA and malB.

ACESSO AO ARTIGO

Documentos Relacionados