We have constructed a plasmid cloning vector, pGB2, which is derived from the Escherichia coli plasmid pSC101. The plasmid, which specifies resistance to spectinomycin and streptomycin, contains unique restriction sites for the enzymes HindIII, PstI, SalI, BamHI, SmaI and EcoRI. pGB2 shows no sequence homology, as detected by DNA-DNA hybridization, to several widely used vectors such as pBR322, pUC8 and phage lambda L47.1. Amongst other applications, DNA fragments can be cloned into the plasmid and then radioactive plasmid DNA can be used as a probe to screen recombinant DNA libraries.