Both the chloroplast and nuclear genomes of Chlamydomonas reinhardi share homology with Escherichia coli genes for transcriptional and translational components.

Considerable DNA sequence homology can be detected between the Escherichia coli genes coding for translational and transcriptional components and both the chloroplast and nuclear genomes of Chlamydomonas reinhardi. Labeled chloroplast DNA was demonstrated to hybridize to DNA fragments of the transducing phages λfus3 and λspc2 that encode ribosomal proteins of the α and S10 operons. Further, chloroplast DNA probes hybridize to fragments of λrtf (d) 18 that encode the β and β' subunits of RNA polymerase. The regions homologous to the ribosomal protein and RNA polymerase genes were located on the chloroplast DNA physical map by probing restriction fragments of chloroplast DNA with phage or plasmid fragments carrying these E. coli genes. Probing nuclear DNA with bacterial gene probes revealed DNA fragments homologous to elongation factor and ribosomal protein genes. Most surprisingly, sequences homologous to the β subunit of RNA polymerase were found not only in chloroplast DNA but in nuclear DNA as well.