Molecular model for elongation of the murein sacculus of Escherichia coli.

Labeling experiments are presented that suggest that new (radioactive) strands of murein are initially inserted adjacent to old strands. After 8 min, new strands start to be inserted adjacent to the previously inserted radioactive strands. Analysis of these data suggests that, for Escherichia coli to double the length of the sacculus in each generation, about 90 separate membrane-bound enzyme complexes travel unidirectionally around the circumference of the cell. They travel at a constant rate, six times each generation, synthesizing, inserting, and crosslinking two strands of murein at a time, thereby doubling the length of the sacculus.