A comparison of the effects of alkylating agents 1,3-bis(2-chloroethyl)-1-nitrosourea, 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea and nitrogen mustard on nuclear RNA synthesis/and processing

Abstract

The effect of three alkylating agents on the RNA metabolism of HeLa cells were compared. The agents, nitrogen mustard (HN 2), 1,3-bis(2-chloroethyl)-1-nitrosourea and 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea, are quite different in their modes of inhibition and relatively specific in their effects on RNA synthesis and processing. Nitrogen mustard severely inhibits the formation of 45 S ribosomal RNA precursor in the nucleolus by producing shortened RNA chains. The remnant 45 S RNA that is produced appears to process normally at least as far as 32 S. The drug produces shortened nucleoplasmic RNA (HnRNA) molecules. Cytoplasmic messenger RNA is completely inhibited, presumably as a result of the aberrant nucleoplasmic synthesis. 1,3-bis(2-chloroethyl)-1-nitrosourea has little immediate effect on ribosomal precursor RNA synthesis in the nucleolus. However, subsequent processing of the 45 S precursor RNA is severely inhibited. Prolonged exposure to the drug leads to an inhibition of 45 S RNA synthesis, possibly because of the block in the processing step. The drug has little effect on HnRNA synthesis. The addition of poly(A) to HnRNA is normal. However, the subsequent appearance of poly(A)-containing cytoplasmic mRNA is severely inhibited. 1-(2-Chloroethyl)-3-cyclohexyl-1-nitrosourea directly inhibits the synthesis of 45 S precursor RNA in the nucleolus. The processing of such RNA as is formed is also inhibited. In contrast, it has little or no effect on HnRNA synthesis and does not affect the appearance of poly(A)-containing cytoplasmic message.