Long- and short-patch gene conversions in Streptococcus pneumoniae transformation.

In pneumococcal transformation some point mutations are integrated by an excision-repair pathway which switches the heteroduplex DNA into homoduplex. This transfer of information is a gene conversion. We have reviewed some of the properties of this system especially those relating to heteroduplex specificity and given evidence that this extends over several kilobases of DNA. We then describe a new process of conversion in pneumococcal transformation which occurs over a very short distance (5 to 27 base-pairs) and is triggered by a single site mutation resulting from the transversion 5'-ATTCAT...to 5'...ATTAAT... Only one of the two heteroduplexes 5'...A...3'/3'...G...5', is converted.