["Silent" marker effect in T4-phage recombination]

Effects of the silent sites of heterozygosity on genetic recombination have been studied in crosses between the markers localized in the proximal segment of rIIB gene of T4 phage. It was found that silent markers could inhibit as well as stimulate genetic recombination. For the expression of these marker effects, the distance between the silent marker and those for which recombination was being monitored, appeared to be critical. There were no marker interference in the crosses in which an influencing marker was separated from recombining ones by a distance exceeding the length of DNA segment involved in single mismatch-repair event. The most prominent marker effects were observed when an influencing marker and recombining one were linked closely enough to form a mutual mismatched region. From the results obtained it is evident that the target which is recognized by mismatch-repair mechanism is formed from DNA strands originating from both parents, and both strands of the heteroduplex are essential for the recognition.