Sensitivity to UV irradiation conferred by recF143 was partially suppressed by recA441 (also known as tif-1). A temperature-conditional component depended on uvrA function and is thought to involve thermal induction of excision repair enzymes. In a uvrA6 mutant, a temperature-independent component of suppression was seen. This is thought to indicate that recA441 also caused temperature-independent changes in recA activity. Two hypotheses are offered to explain how recA441 produced both thermosensitive and thermoindependent effects.