Repression of β-actin synthesis and persistence of ribosomal protein synthesis after infection of HeLa cells by herpes simplex virus type 1 infection are under translational control

Abstract

Synthesis and assembly of ribosomal proteins into mature ribosomes persist late after infection of cells with herpes simplex virus type 1, while synthesis of β-actin is drastically shut off. Since mRNAs encoding ribosomal proteins and β-actin undergo concomitant degradation in infected HeLa cells, we have advanced the hypothesis that translation of the remaining mRNAs is differentially controlled after infection. The behaviour of mRNAs for three ribosomal proteins and for β-actin was investigated during the course of infection. In uninfected cells, β-actin mRNAs are associated with large polyribosomes, while only a part of ribosomal protein mRNAs are present in polyribosomes. In the course of infection, β-actin mRNAs are released from the ribosomes and are sequestered with 40S ribosomal subunits. Simultaneously, ribosomal protein mRNAs become associated with an increased number of ribosomes, even late in infection. In addition, virally induced phosphorylation of ribosomal protein S6 is more efficient in pre-existing ribosomes than in newly assembled ribosomes. These results indicate that in infected cells (i) translation of β-actin mRNA is selectively inhibited at a step necessary for binding the 60S ribosomal subunits; (ii) the rate of initiation of translation of ribosomal protein mRNAs increases after infection; and (iii) it is likely that translation of ribosomal protein mRNAs takes place preferentially on pre-existing ribosomes.