A small, unstable RNA molecule of Escherichia coli: spot 42 RNA. II. Accumulation and distribution.

We have studied the accumulation and distribution of a small, unstable RNA molecule of Escherichia coli called spot 42 RNA (Ikemura &; Dahlberg, 1973b). This molecule has sequence and structural features characteristic of messenger RNAs and leader RNAs (Sahagan &; Dahlberg, 1979). It is present in 100 to 200 copies per cell when cells are grown in media supplemented with glucose. Although it accumulates in cells that have been deprived of an essential amino acid or phosphate or ammonium ions, the amount of spot 42 RNA is greatly reduced when cells are grown on non-glucose carbon sources or when cyclic AMP is added to a glucose-grown culture. Thus accumulation of spot 42 RNA is inversely proportional to the intracellular concentration of cAMP.About half of the spot 42 RNA in a cell is isolated in association with bacterial nucleoids. It is the only 4 to 6 S RNA which is enriched in this fraction. This molecule also cofractionates with 5 S ribosomal RNA during the preparation of ribosomes and ribosome fractions.The possibility that spot 42 RNA is a leader sequence whose level of accumulation is modulated by the intracellular level of cAMP is discussed.