A comparison of the genetic and physical size of the streptomycin resistance locus in Pneumococcus.

Polyacrylamide gel electrophoresis of the 30S ribosomal proteins derived from six streptomycin resistant strains indicates that each mutation alters the same ribosomal protein (str-r protein). Preliminary data utilizing SDS gels indicates that the str-r protein has a molecular weight between 10,000 and 20,000 daltons. No significant differences could be detected between the molecular weight of the str-r protein when it is derived either from a sensitive or from a resistant strain, including those derived from strains carrying multisite mutations of different genetic size. We have estimated the size of the multisite str-r mutations to be less than 30 base pairs. Two factor crosses with str-r markers in the trans position demonstrate recombination frequencies expected of closely linked, intragenic markers although cotransfer frequencies, of these same markers from the cis position, are very low. It is concluded that the cotransfer frequencies represent a marker effect and possible explanations are discussed. A reinterpretation of the genetic map of the pneumococcal str-r locus is presented.