On representation of the t-J model via spin-charge variables

We show that the t-J Hamiltonian is not in general reduced to H(S,f), where S and f stand for independent ([S,f]=0) SU(2) (spin) generators and spinless fermionic (hole) field, respectively. The proof is based upon an identification of the Hubbard operators with the generators of the su(2|1) superalgebra in the degenerate fundamental representation and ensuing SU(2|1) path integral representation of the partition function.Comment: 15 pages, latex, no figure

Proofreading of pre-40S ribosome maturation by a translation initiation factor and 60S subunits

In the final steps of yeast ribosome synthesis, immature translation-incompetent pre-40S particles that contain 20S pre-rRNA are converted to the mature translation-competent subunits containing the 18S rRNA. An assay for 20S pre-rRNA cleavage in purified pre-40S particles showed that cleavage by the PIN domain endonuclease Nob1 was strongly stimulated by the GTPase activity of the cytoplasmic translation initiation factor eIF5b/Fun12. Cleavage of the 20S pre-rRNA was also inhibited in vivo and in vitro by blocking binding of Fun12 to the 25S rRNA through specific methylation of its binding site. Cleavage competent pre-40S particles stably associate with Fun12 and form 80S complexes with 60S ribosomal subunits. We propose that recruitment of 60S subunits promotes GTP-hydrolysis by Fun12, leading to structural rearrangements within the pre-40S particle that bring Nob1 and the pre-rRNA cleavage site together