A subclass of Ras proteins that regulate the degradation of I kappa B

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.