During protein deprivation the brain, neural tube and extraembryonic membrane of the early chick embryo rapidly lose label from rRNA and protein. At the same time no decrease in the quantity of these macromolecules can be found in these regions. On the other hand, ribosomal turnover can not be demonstrated in the somites or heart of protein-deprived embryos nor in any region of growing embryos. During 36 h culture on complete growth medium, the brain, neural tube and membrane double their ribosome/cell ratio, while this ratio remains constant in the heart and somite regions. This ratio also remains constant in all regions during 36 h culture on protein-deprivation medium. The rapid ribosomal turnover seen in the sensitive regions of the starved embryo appears to be a mechanism whereby rRNA/DNA is held constant during growth inhibition of a previously rapidly multiplying cell population.
展开▼
