Marker discrimination in transformation and mutation of pneumococcus.

Earlier investigations of pneumococcal transformation revealed a function (hex(+)) responsible for severely reducing the transformation yield of certain markers. A mutational alteration (hex(-)) responsible for the loss of this function has been transferred into a hex(+) strain to permit a comparison of the hex(+) and hex(-) phenotypes in an isogenic background. The loss of the hex(+) function results both in a loss of the capacity to eliminate the low efficiency markers in transformation and a substantial increase in the spontaneous mutation rate. These properties of the hex(-) strain could result from the loss of a capacity to eliminate certain classes of mismatched base pairs that occur as intermediates in both transformation and mutagenesis.