Small guanosine triphosphatases, typified by the mammalian Ras proteins, pl
ay major roles in the regulation of numerous cellular pathways. A subclass
of evolutionarily conserved Ras-Like proteins was identified, members of wh
ich differ from other Ras proteins in containing amino acids at positions 1
2 and 61 that are similar to those present in the oncogenic forms of Ras. T
hese proteins, kappa B-Ras1 and kappa B-Ras2, interact with the PEST domain
s of I kappa B alpha and I kappa B beta [inhibitors of the transcription fa
ctor nuclear factor kappa B (NF-kappa B)] and decrease their rate of degrad
ation. In cells, kappa B-Ras proteins are associated only with NF-kappa B:I
kappa B beta complexes and therefore may provide an explanation for the sl
ower rate of degradation of I kappa B beta compared with I kappa B alpha.