No abstract

No abstract

In order to gain a better understanding of the interaction between the chloroplast and nuclear genomes in controlling the expression of plastid genes and the biosynthesis of chloroplast proteins, maize (Zea mays) Plastids of higher plants can differentiate into a number of forms including photosynthetically active chloroplasts, starchstoring amyloplasts, and carotenoid crystal-containing chloroplasts. Plastid metabolism requires the products of hundreds of genes but the plastid genome encodes many fewer. Most plastid proteins are products of the nuclear-cytoplasmic system; they must be imported from outside of the organelle. Genes for polypeptides of multimeric components of plastids including ribosomes, RuBP3 carboxylase/oxygenase, CF1 (coupling factor one for photophosphorylation), thylakoids, and others are dispersed in the nuclear and plastid genomes. Such dispersal of genes seems to be a feature of eukaryotic cell biology (2). Understanding the mechanisms for integration of nuclear and organelle gene expression, particularly for these multimeric components, is a central problem of eukaryotic cell biology.

No abstract

Gamma radiation-induced gene rearrangements at the Chinese hamster ovary cell locus coding for the purine salvage enzyme adenine phosphoribosyl transferase (APRT) consist of both simple deletions and more complex alterations that are presumably the result of multiple strand breaks. To characterize these mutations at the DNA sequence level, fragments altered by deletion and insertion mutations were obtained by cloning in lambda phage vectors or by using the polymerase chain reaction. The radiation-induced deletions characterized here eliminate 3-4 kb and have at least one breakpoint in an AT-rich region or near short direct or inverted repeats. Insertions involve small fragments (102 and 456 bp) of repetitive DNA that appear to be related to B2 (short interspersed repetitive) and long interspersed repeat families. The novel fragments bear little resemblance to each other or to sequences at the integration sites, and their introduction is accompanied by a small target site deletion.