REPRESSION OF BETA-ACTIN SYNTHESIS AND PERSISTENCE OF RIBOSOMAL-PROTEIN SYNTHESIS AFTER INFECTION OF HELA-CELLS BY HERPES-SIMPLEX VIRUS TYPE-1 INFECTION ARE UNDER TRANSLATIONAL CONTROL

Synthesis and assembly of ribosomal proteins into mature ribosomes per sist late after infection of cells with herpes simplex virus type 1, w hile synthesis of beta-actin is drastically shut off. Since mRNAs enco ding ribosomal proteins and beta-actin undergo concomitant degradation in infected HeLa cells, we have advanced the hypothesis that translat ion of the remaining mRNAs is differentially controlled after infectio n. The behaviour of mRNAs for three ribosomal proteins and for beta-ac tin was investigated during the course of infection. In uninfected cel ls, beta-actin mRNAs are associated with large polyribosomes, while on ly a part of ribosomal protein mRNAs are present in polyribosomes. In the course of infection, beta-actin mRNAs are released from the riboso mes and are sequestered with 40S ribosomal subunits. Simultaneously, r ibosomal protein mRNAs become associated with an increased number of r ibosomes, even late in infection. In addition, virally induced phospho rylation of ribosomal protein S6 is more efficient in preexisting ribo somes than in newly assembled ribosomes. These results indicate that i n infected cells (i) translation of beta-actin mRNA is selectively inh ibited at a step necessary for binding the 60S ribosomal subunits; (ii ) the rate of initiation of translation of ribosomal protein mRNAs inc reases after infection and (iii) it is likely that translation of ribo somal protein mRNAs takes place preferentially on pre-existing ribosom es.