CLONING AND EXPRESSION OF PNEUMOCOCCAL GENES IN STREPTOCOCCUS-PNEUMONIAE

An overview of gene cloning in Streptococcus pneumoniae is presented. The advantages of such cloning, especially for pneumococcal genes, are enumerated. The molecular fate of DNA in transformation of S. pneumon iae, in particular, the conversion of DNA to single-strand segments on entry, determines the mechanisms for plasmid establishment and intera ction with the chromosome. One of these mechanisms, the chromosomal fa cilitation of plasmid establishment, is useful for obtaining recombina nt plasmids and for introducing an allele from the chromosome into a p lasmid. The difference between linear and circular synapsis of donor D NA strands with the chromosome is illustrated. Circular synapsis can g ive rise to circular integration, which is useful for insertional muta genesis of chromosomal genes, for coupled cloning in Escherichia coli, and for sequential cloning of DNA along the pneumococcal chromosome. Cloning in S. pneumoniae is not notably affected by DNA mismatch repai r or restriction systems in the host cell. Unusual features of gene ex pression in S. pneumoniae are discussed. Transcription begins most oft en at promoters with extended -10 sequences, and in a small but signif icant number of cases, translation does not require a ribosome-binding site with a Shine-Dalgarno sequence.