NRAS and infection: In the absence of BRAF inhibition, the combination of MmuPV1 infection and concomitant UVB irradiation did not result in mutations in codons 12/13 and 61 of Hras1, Kras and Nras (MU mice: all 0%; 0/4 each), and UVB irradiation alone likewise did not induce mutations in any of the investigated RAS isoforms (U mice: all 0%; 0/1 each).