Complementation tests were carried out with group I mutant ts29 and group II mutant ts39. Symbols + and − refer to growth at 42°C. The phage clones and plasmids used were as follows: A-1, Kohara phage 652; A-2, pUC19 containing the 6-kb KpnI fragment (p652-0); A-3, pUC19 containing the 5.4-kb KpnI-SmaI fragment (p652-1); B-1, Kohara phage 560; B-2, pMW119 containing the 7-kb EcoRI fragment (p560-0); B-3, pMW119 containing the 4-kb EcoRI-HpaI fragment (p560-1); B-4, pMW119 containing the 1.5-kb EcoRI-SacI fragment (p560-2); B-5, pMW119 containing the 2.5-kb SmaI-HpaI fragment (p560-3); C-1, Kohara phage 648; C-2, pHSG576 containing the 6-kb EcoRI fragment (p648-0); and C-3, pHSG576 containing the 5.5-kb EcoRI-BamHI fragment (p648-1).