if semi-conservative dna synthesis on a template still containing unexcised lesions is responsible for introducing mutations and if replication of the gene of interest , e.g. , hypoxanthine ( guanine ) phosphoribosyltransferase ( hprt ) for thioguanine resistance or the elongation factor 2 ( ef-2 ) for diphtheria toxin resistance , occurs at a particular time during s-phase , it should be possible to shorten the time available for such repair by synchronizing cells and irradiating them just as the gene is to be replicated .
C0080129
s-phase
C0007634
cells