Structural basis for the molecular recognition of polyadenosine RNA by Nab2 Zn fingers.

The yeast poly(A) RNA binding protein, Nab2, facilitates poly(A) tail length regulation together with targeting transcripts to nuclear pores and their export to the cytoplasm. Nab2 binds polyadenosine RNA primarily through a tandem repeat of CCCH Zn fingers. We report here the 2.

Structural basis for polyadenosine-RNA binding by Nab2 Zn fingers and its function in mRNA nuclear export.

Polyadenylation regulation and efficient nuclear export of mature mRNPs both require the polyadenosine-RNA-binding protein, Nab2, which contains seven CCCH Zn fingers. We describe here the solution structure of fingers 5-7, which are necessary and sufficient for high-affinity polyadenosine-RNA binding, and identify key residues involved. These Zn fingers form a single structural unit.

Structural basis for the assembly and disassembly of mRNA nuclear export complexes.

Most of the individual components of the nuclear elements of the gene expression pathway have been identified and high-resolution structural information is becoming available for many of them. Information is also starting to become available on the larger complexes they form and is beginning to give clues about how the dynamics of their interactions generate function. Although the translocation of export-competent messenger ribonucleoprotein particles (mRNPs) through the nuclear pore transport channel that is mediated by interactions with nuclear pore proteins (nucleoporins) is relatively well understood, the precise molecular mechanisms underlying the assembly of export-competent mRNPs in the nucleus and their Dbp5-mediated disassembly in the cytoplasm is less well defined.

Evidence for an allosteric mechanism of substrate release from membrane-transporter accessory binding proteins.

Numerous membrane importers rely on accessory water-soluble proteins to capture their substrates. These substrate-binding proteins (SBP) have a strong affinity for their ligands; yet, substrate release onto the low-affinity membrane transporter must occur for uptake to proceed. It is generally accepted that release is facilitated by the association of SBP and transporter, upon which the SBP adopts a conformation similar to the unliganded state, whose affinity is sufficiently reduced.

Structure and function of the universal stress protein TeaD and its role in regulating the ectoine transporter TeaABC of Halomonas elongata DSM 2581(T).

The halophilic bacterium Halomonas elongata takes up the compatible solute ectoine via the osmoregulated TRAP transporter TeaABC. A fourth orf (teaD) is located adjacent to the teaABC locus that encodes a putative universal stress protein (USP). By RT-PCR experiments we proved a cotranscription of teaD along with teaABC.

1.55 A structure of the ectoine binding protein TeaA of the osmoregulated TRAP-transporter TeaABC from Halomonas elongata.

TeaABC from the moderate halophilic bacterium Halomonas elongata belongs to the tripartite ATP-independent periplasmic transporters (TRAP-T), a family of secondary transporters functioning in conjunction with periplasmic substrate binding proteins. TeaABC facilitates the uptake of the compatible solutes ectoine and hydroxyectoine that are accumulated in the cytoplasm under hyperosmotic stress to protect the cell from dehydration. TeaABC is the only known TRAP-T activated by osmotic stress.