Biomedical subjects

Mark A Bayfield

Publications and source records attributed to Mark A Bayfield.

3 recordsLinked to original sources

PubMed2006

Separate RNA-binding surfaces on the multifunctional La protein mediate distinguishable activities in tRNA maturation.

By sequence-specific binding to 3' UUU-OH, the La protein shields precursor (pre)-RNAs from 3' end digestion and is required to protect defective pre-transfer RNAs from decay. Although La is comprised of a La motif and an RNA-recognition motif (RRM), a recent structure indicates that the RRM beta-sheet surface is not involved in UUU-OH recognition, raising questions as to its function. Progressively defective suppressor tRNAs in Schizosaccharomyces pombe reveal differential sensitivities to La and Rrp6p, a 3' exonuclease component of pre-tRNA decay. 3' end protection is compromised by mutations to the La motif but not the RRM surface. The most defective pre-tRNAs require a second activity of La, in addition to 3' protection, that requires an intact RRM surface. The two activities of La in tRNA maturation map to its two conserved RNA-binding surfaces and suggest a modular model that has implications for its other ligands.

Amino Acid Sequence↗

PubMed2006

The La protein-RNA complex surfaces.

A recent issue of Molecular Cell reported that the typical nucleic acid binding surfaces of the RRM and winged-helix motifs, although present in the RNA binding protein La, are not used to engage its best-characterized ligand, 3' UUU-OH. Instead, La uses edgewise and backsides of these motifs for UUU-OH recognition, leaving open their typical surfaces for other potential interactions. These observations provide a framework for appreciating the various activities attributed to this ubiquitous nuclear phosphoprotein, which include its principal function, snRNA 3' end protection, in addition to mRNA-related and RNA chaperone-like activities, as well as DNA and chromatin-associated activity.

Amino Acid Motifs↗

PubMed2004

The A2453-C2499 wobble base pair in Escherichia coli 23S ribosomal RNA is responsible for pH sensitivity of the peptidyltransferase active site conformation.

Peptide bond formation, catalyzed by the ribosomal peptidyltransferase, has long been known to be sensitive to monovalent cation concentrations and pH. More recently, we and others have shown that residue A2451 in the peptidyltransferase center of the Escherichia coli 50S ribosomal subunit changes conformation in response to alterations in pH, depending on ionic conditions and temperature. Two wobble pairs, A2453-C2499 and A2450-C2063, have been proposed as potential candidates to convey pH-dependent flexibility to the peptidyltransferase center. Each is presumed to possess a near-neutral pK(a), and both lie in proximity to A2451. We show through mutagenesis and chemical probing that the identity of the A2453-C2499 base pair, but not the A2450-C2063 base pair, is critical for the pH-dependent structural rearrangement of A2451. We conclude that, while the A2453-C2499 base pair may be important for maintaining the structure of the active site in the E.coli peptidyltransferase center, its lack of conservation makes it, and consequently its near-neutral pK(a), unlikely to contribute to function during peptide bond formation.

Adenine↗