title: Activation of protein synthesis by microsomes from aging beet disks.
abstract: Microsomal fractions isolated from sterile, aged disks of red beetroot incorporate leucine into protein when supplemented with the supernatant fraction, ATP, GTP, and KCl; the incorporation is sensitive to RNase and is not due to bacteria. The microsomal activity is inhibited by puromycin and cycloheximide but is virtually insensitive to both d-threo and l-threo-chloramphenicol, as predicted from physiological studies.Microsomes isolated from fresh disks have much lower incorporating ability than those from disks aged for 1 or 2 days; maximal activity occurs when the rate of protein synthesis by the intact disks is highest. The low activity of fractions from fresh disks is attributable to a deficiency in the microsomal fraction and not to the supernatant fraction; it is not due to a dissociable inhibitor. The RNA content of the microsomal fraction increases with aging and so the increase in incorporating ability may be due to a synthesis of messenger RNA induced by slicing, rather than to an activation of pre-existing messenger. These results support the view that the aging phenomenon involves a derepression of gene activity.
authors.affiliation: Department of Botany, University of Aberdeen, Aberdeen, Scotland.
authors.forename: R J
authors.initials: RJ
authors.lastname: Ellis
authors.forename: I R
authors.initials: IR
authors.lastname: Macdonald