Isolation of chromosomal DNA

The bulk DNA of R.sphaeroides was isolated basically by the procedure of Saito and Miura［23］.The total bulk DNA was digested with Bam HI and separated on an agarose gel.

Radioactive labeling of RNA and DNA.Total R.sphaeroides RNA was radiolabeled in vitro by phosphorylating the 5'-OH groups produced by partial alkaline hydrolysis of RNA with 32P from［γ-32P］ATP with T4 polynucleotide kinase by the method of Bogorad et al.［4］.RNA samples for Southern hybridization were adjusted to equal specific radioactivity（106 cpm/μg）.The plasmid DNA or DNA fragment（see Table 1）used for dot blot and Northern hybridizations were labeled with［α-32P］dCTP by nick translation by the protocol of Bethesda Research Laboratories，Gaithersburg，Md.The labeled DNA and［α-32P］dCTP were separated with a spun column of Sephadex G-50 by the method of Maniatis et al.［18］.

Table 1　Plasmids used for probing photosynthetic genes of R.sphaeroides

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