FIG. 1.

Strategy for construction of a random mutagenic library of insertion plasmids. Elements of pEVP3 indicated are ori, a replication origin active in E. coli but not in S. pneumoniae; cat, the gene for chloramphenicol acetyltransferase, which confers Cm^r to both hosts; and ′lacZ, the promoterless gene for β-galactosidase. Small open boxes, 300-bp pneumococcal fragments; horizontal lines, linear pEVP3 molecules; dots, replication origins; vertical line, vector-vector joint within a concatemer of pEVP3 and inserts. conc., concentrations.