[The effect of cycloheximide on incorporation of newly formed mRNA into membrane-bound polyribosomes in rat liver cells].

Incorporation kinetics of new synthesized mRNA into free and endoplasmic membrane-bound polyribosomes in the absence of normal translation (when protein synthesis in inhibited by 98% with cycloheximide) is studied. mRNA is found to incorporate into both free and bound polyribosomes. Relative content of new synthesized membrane-bound polyribosomes in the presence of cycloheximide within 2.5-4.5 hours is by 30-40% lower as compared with the control. This fact can be explained either by the absence of a growing peptide of a sufficient length, which is necessary for the formation of a part of membrane-bound polyribosomes, or by a restricted number of attachment sites on membranes as a result of delayed translation of mRNA in pre-existed polyribosomes. It is suggested that 1) the growing peptide in liver cells is responsible for the recognition of a membrane only under the formation of only one type of membrane-bound polyribosomes, or 2) the formation of all bound polyribosomes has a single mechanism and the growing peptide does not participates in the membrane recognition.