Alterations of RNA metabolism in sea urchin embryos by an inhibitor of protein synthesis initiation

Abstract

An inhibitor of the initiation of protein synthesis, 2-(4 methyl-2,6 dinitroanilino)-N- methyl propionamide, (MDMP), inhibits incorporation of amino acids by 85–95% without altering the rate of incorporation of uridine into sea-urchin-hatched blastula embryos. Since the inhibition is readily reversible up to at least 90 min after addition, extensive secondary effects are unlikely. Newly synthesized RNA accumulates in polyribosome-like structures in amount and with a size distribution very similar to the control. The polyadenylation of total, cytoplasmic and polyribosomal RNA are only slightly different from the controls. While the size distribution of 9-S to approx. 30-S RNA is about the same, there is relatively less low molecular weight RNA (approx. 4-S). There is also a greater accumulation of >30- S RNA in the cytoplasm of treated embryos due either to leakage and/or improper processing of nuclear RNA. The latter possibility is consistent with the decrease in 4-S RNA which is a presumed degradation product of nuclear HnRNA. While the initial rate of RNA synthesis and much of the accumulation of RNA in polyribosomes are not affected, the inhibition of protein synthesis per se or a secondary effect of MDMP results in altered patterns of RNA transport and processing.