Biomedical subjects
Publications and source records attributed to James Dahlberg.
Two recently published papers (Takano et al., 2005 and Shaheen and Hopper, 2005) demonstrate that in S. cerevisiae, cytoplasmic tRNAs can be transported into the nucleus. This retrograde movement may expose mature tRNAs to nuclear proofreading or it may regulate tRNA availability in response to amino acid availability.
The partitioning of cells by a nuclear envelope ensures that precursors of ribosomes do not interact prematurely with other components of the translation machinery. Ribosomal subunits are assembled in nucleoli and exported to the cytoplasm in a CRM1/Ran-GTP-dependent fashion. Export of the large (60S) subunit requires a shuttling adaptor protein, NMD3, which binds to mature, correctly folded subunits. Immature or defective particles do not bind NMD3 and thus are excluded from the export pathway. This structural proofreading is extended into the cytoplasm, where it is believed that several energy-requiring steps release shuttling factors from the subunit, allowing it to function in translation.