RESTRICTION INVIVO .4. EFFECT OF RESTRICTION OF PARENTAL DNA ON THE EXPRESSION OF RESTRICTION ALLEVIATION SYSTEMS IN PHAGE-T4

Under restricting conditions expression of early T4 genes is determined in part by the location of the particular gene relative to the cleavage site. Some genes are inactivated directly by cleavage of the DNA. Other genes are inactivated by secondary exonucleolytic degradation of cleaved DNA. A third class of genes continues to be expressed from the small fragments which remain after the exonucleolytic degradation of the cleaved fragments. Expression of phage genes coding for the inhibitors of the restriction endonuclease and restriction exonuclease are prevented by endonucleolytic cleavage and exonucleolytic degradation, respectively. © 1979.