DNA-binding proteins and structural characteristics of chloroplast nucleoids

A comparative analysis of proteins from chloroplast nucleoids was performed in two higher-plant species (Pisum sativum L. and A rabidopsis thaliana L. ) and a green alga Chlamydomonas reinhardtii Dang. In the nucleoids of the higher plants and the alga, 26-27 proteins were detected with their mol wts ranging from 10 to more than 94 kD. In all the species tested, the distrib ution of nucleoid proteins by their mol wts was similar, especially between the predominant proteins with mol wts of 10 to 40 kD. Six DNA-binding prot eins (12-18 kD) were detected in nucleoids from Ch. reitthardtii chloroplas ts after in vivo covalent cross-linking between chloroplast DNA and protein s. Under an electron miscroscope, some regular structures resembling nucleo some-like particles of bacterial cells were revealed.