Abstract
The unicellular red alga Cyanidioschyzon merolae is a primitive eukaryote conserving some bacterial DNA binding protein gene in the plastid genome. A homologue of bacterial histone-like protein HU is present in the plastid nucleoids of C. merolae, and this protein has ability to compact DNA, while sulfite reductase (SiR) compacts DNA in the nucleoids of pea plastids. We isolated nucleoids from the cyanobacterium Anabaena PCC 7120 and the plastids of C. merolae, moss and pea. We compared the basic properties of in vitro transcription and effect of DNA-binding proteins on transcription activity of each nucleoids. Though SiR repressed the transcription activity of all nucleoids, HU activated transcription activity of nucleoids of Anabaena and C. merolae. The HU/DNA complex was physically different from the SiR/DNA complex. Nucleoid proteins have different roles in different lineages.
