Two precursor 5S RNA species in Bacillus licheniformis: characterization and partial analysis of primary structure

The induction of HAD-like phosphatases by multiple signaling pathways confers resistance to the metabolic inhibitor 2-deoxyglucose

Anti-cancer strategies that target the glycolytic metabolism of tumors have been proposed. The glucose analog 2-deoxyglucose (2DG) is imported into cells and, after phosphorylation, becomes 2DG-6-phosphate, a toxic by-product that inhibits glycolysis. Using yeast as a model, we performed an unbiased mass spectrometry-based approach to probe the cellular effects of 2DG on the proteome and study resistance mechanisms to 2DG. We found that two phosphatases that target 2DG-6-phosphate were induced upon exposure to 2DG and participated in 2DG detoxification. Dog1 and Dog2 are HAD (haloacid dehalogenase)-like phosphatases, which are evolutionarily conserved. 2DG induced Dog2 by activating several signaling pathways, such as the stress response pathway mediated by the p38 MAPK ortholog Hog1, the unfolded protein response (UPR) triggered by 2DG-induced ER stress, and the cell wall integrity (CWI) pathway mediated by the MAPK Slt2. Loss of the UPR or CWI pathways led to 2DG hypersensitivity. In contrast, mutants impaired in the glucose-mediated repression of genes were 2DG resistant because glucose availability transcriptionally repressed DOG2 by inhibiting signaling mediated by the AMPK ortholog Snf1. The characterization and genome resequencing of spontaneous 2DG-resistant mutants revealed that DOG2 overexpression was a common strategy underlying 2DG resistance. The human Dog2 homolog HDHD1 displayed phosphatase activity toward 2DG-6-phosphate in vitro and its overexpression conferred 2DG resistance in HeLa cells, suggesting that this 2DG phosphatase could interfere with 2DG-based chemotherapies. These results show that HAD-like phosphatases are evolutionarily conserved regulators of 2DG resistance.

Nucleotide sequence analysis of precursor 5S RNA from Bacillus licheniformis

The complete nucleotide sequences of the various precursor 5S RNA species occurring in Bacillus licheniformis have been elucidated. The B. licheniformis precursors contain a 5'-precursor-specific segment of 95 nucleotides which is four times as long as the corresponding segment of the p5S RNAs from the closely related strains B. subtilis (Sogin, M.L., Pace, N.R., Rosenberg, M., Weissman, S.M. (1976) J. Biol. Chem. 251, 3480-3488) and Bacillus Q (Stiekema, W.J., Raué, H.A., Planta, R.J. (1980) Nucl. Ac. Res. 8, 2193-2211). However, fourteen of the sixteen nucleotides at the 5'-end are identical in the precursors from all three strains. These conserved nucleotides can form a stem and loop structure which is likely to play an important role in the biosynthesis of 5S RNA. Extension secondary and tertiary structure is present in the 5'-precursor-specific segment as concluded from the results of digestion with RNAase T1 both of the isolated segment and the intact precursors. No sequence homology exists between the 3'-precursor-specific segments of the B. licheniformis precursors and those of the other two strains except for a stretch of U residues at the 3-terminus. This stretch of U residues is not immediately preceded by a hairpin loop, however, as expected for a transcription termination signal (20). The question whether the precursors have already undergone processing at the 3'-end, therefore, remains open. The total number of genetically distinct precursor species in B. licheniformis is at least five and at most ten. Most likely each ribosomal RNA cistron produces a separate p5S RNA as is also the case in Bacillus Q.

Sequence analysis and in vitro maturation of five precursor 5S RNAs from Bacillus Q

Bacillus Q, which is closely related to B. subtilis, contains at least six different precursors of 5S rRNA. The complete nucleotide sequences of four of these precursors, as well as the major part of the sequence of a fifth one, have been determined. They all contain the same 5'-terminal non-conserved segment which is to a large degree homologous with the corresponding segment of the B. subtilis p5S RNAs (Sogin, M.L., Pace, N.R., Rosenberg, M., Weissman, S.M. (1976) J. Biol. Chem. 251, 3480-3488). On the other hand the 3'-terminal non-conserved sequences of the various Bacillus Q precursors show considerable differences both in length and in nucleotide sequence, while there is also little or no homology with the 3'-terminal non-conserved sequence of the B. subtilis precursors. Bacillus Q p5S RNAs do not possess tetranucleotide repeats around the sites which are cleaved during maturation, as does B. subtilis p5S RNA. Like in B. subtilis, however, the cleavage sites are contained within a double-helical region of the precursor molecules. Crude RNAse M5 isolated from various Bacillus strains can maturate the Bacillus Q p5S RNAs with high efficiency. Despite considerable differences in primary structure between the precursors from the various strains, each RNAs M5 preparation can maturate all these precursors with about the same efficiency.

Occurrence in Bacillus licheniformis of two species of 5-S RNA with multiple differences in primary structure

Bacillus licheniformis was found to contain two species of 5-S RNA. One of these, the primary structure of which has been published previously [H. A. Raué, T.J. Stoof and R.J. Planta (1975) Eur. J. Biochem. 59, 35--42] accounts for 80--90% of the total cellular amount of 5-S RNA. The other one, comprising 10--20% of the total amount, differs in primary structure from the major species at eight positions. All base changes are either purine leads to purine or pyrimidine leads to pyrimidine substitutions. Half of the changes are located within the 5'-terminal part (15 nucleotides) of the molecule, the other half in the 3'-terminal region (22 nucleotides). At least one of the base changes is in a region which in B. subtilis has been implicated in processing of precursor 5-S RNA. The data are consistent with the existence of a single 5-S RNA cistron with a primary structure different from that of all other 5-S RNA cistrons in B. licheniformis.

Nucleotide sequence of 5-S RNA from Bacillus licheniformis

The complete nucleotide sequence of 5-S RNA from Bacillus licheniformis was determined by analysis of complete and partial digests obtained with either T1 or pancreatic ribonuclease. The molecule was found to have a length of 116 nucleotides and may possess a minor sequence heterogeneity. There is a large degree of homology between the sequence of B. licheniformis 5-S RNA and those published for 5-S RNA from B. megatherium and B. stearothermophilus. The difference between the three 5-S RNA species are limited mainly to the two terminal and one internal sequence. B. licheniformis 5-S RNA contains the sequence U95-G-A-G-A-G100, which in B. subtilis has been implicated in the processing of precursor 5-S RNA. Possible models for the secondary structure of prokaryotic 5-S RNA are discussed on the basis of the results of limited digestion of B. licheniformis 5-S RNA by ribonuclease T1.