Plant Science Innovation, Center for


Date of this Version

May 1993


Published in Plant Physiology, Vol 102, Issue 1 (May 1993), pp. 145-153. Copyright © 1993 by American Society of Plant Biologists. The American Society of Plant Biologists does not allow its publications to be archived in an institutional repository. It does, however, provide a free link to full-text content on its own site. Please use the following link to access this article:


The occurrence of DNA recombination in plastids of higher plants is well documented. However, little is known at the enzymic level. To begin dissecting the biochemical mechanism(s) involved we focused on a key step: strand transfer between homologous parental DNAs. We detected a RecA-like strand transfer activity in stromal extracts from pea (Pisum sativum L.) chloroplasts. Formation of joint molecules requires Mg2+, ATP, and homologous substrates. This activity is inhibited by excess single-stranded DNA (ssDNA), suggesting a necessary stoichiometric relation between enzyme and ssDNA. In a novel assay with Triton X-100-permeabilized chloroplasts, we also detected strand invasion of the endogenous chloroplast DNA by 32P-labeled ssDNA complementary to the 16S rRNA gene. Joint molecules, analyzed by electron microscopy, contained the expected displacement loops.

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