Thirty eight mutant clones of the colicin indicator strain Escherichia coli K 12 ROW, selected by their insensitivity to any of the colicins E1-E7, were isolated. Comparison of their sensitivity-resistance patterns to colicins E1-E7 enabled us to draw a rough preliminary map of the receptor for E colicins. In this receptor, the highly specific binding site for colicin E1 partially overlaps with the domain shared by all colicins E2 through E7. A specific binding site of this domain appears to be common for colicins E3 and E6; a part of the E3 and E6 binding site is also common for colicins E4 and E5 and a small, least specific, part also for colicins E2 and E7. Using colicin assay experiments, the binding capacity of colicin E receptor mutants could be estimated. A decreased, but not completely lost ability of certain mutants to bind colicins E, correlated to their lowered sensitivity to them, was found. Thus the phenomenon of partial colicin resistance was established, showing that colicin sensitivity--resistance is not a qualitative but a quantitative marker.

Department of Biology Medical Faculty J E Purkynĕ University Brno Czechoslovakia

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Colicins--exocellular lethal proteins of Escherichia coli