Interaction between the RNA-dependent ATPase and poly(A) polymerase subunits of the TRAMP complex is mediated by short peptides and important for snoRNA processing

The RNA exosome is one of the main 3′ to 5′ exoribonucleases in eukaryotic cells. Although it is responsible for degradation or processing of a wide variety of substrate RNAs, it is very specific and distinguishes between substrate and non-substrate RNAs as well as between substrates that need to be 3′ processed and those that need to be completely degraded. This specificity does not appear to be determined by the exosome itself but rather by about a dozen other proteins. Four of these exosome cofactors have enzymatic activity, namely, the nuclear RNA-dependent ATPase Mtr4, its cytoplasmic paralog Ski2 and the nuclear non-canonical poly(A) polymerases, Trf4 and Trf5. Mtr4 and either Trf4 or Trf5 assemble into a TRAMP complex. However, how these enzymes assemble into a TRAMP complex and the functional consequences of TRAMP complex assembly remain unknown. Here, we identify an important interaction site between Mtr4 and Trf5, and show that disrupting the Mtr4/Trf interaction disrupts specific TRAMP and exosome functions, including snoRNA processing.

The Mtr4 ratchet helix and arch domain both function to promote RNA unwinding

Mtr4 is a conserved Ski2-like RNA helicase and a subunit of the TRAMP complex that activates exosome-mediated 3′-5′ turnover in nuclear RNA surveillance and processing pathways. Prominent features of the Mtr4 structure include a four-domain ring-like helicase core and a large arch domain that spans the core. The ‘ratchet helix’ is positioned to interact with RNA substrates as they move through the helicase. However, the contribution of the ratchet helix in Mtr4 activity is poorly understood. Here we show that strict conservation along the ratchet helix is particularly extensive for Ski2-like RNA helicases compared to related helicases. Mutation of residues along the ratchet helix alters in vitro activity in Mtr4 and TRAMP and causes slow growth phenotypes in vivo. We also identify a residue on the ratchet helix that influences Mtr4 affinity for polyadenylated substrates. Previous work indicated that deletion of the arch domain has minimal effect on Mtr4 unwinding activity. We now show that combining the arch deletion with ratchet helix mutations abolishes helicase activity and produces a lethal in vivo phenotype. These studies demonstrate that the ratchet helix modulates helicase activity and suggest that the arch domain plays a previously unrecognized role in unwinding substrates.

Bilateral breast relapse in acute myelogenous leukemia

We present the case of an 11.5-year-old girl with M1 acute myelogenous leukemia (AML) who had isolated extramedullary relapse develop in both breasts 12 months after diagnosis and 7 months off chemotherapy. She received further chemotherapy, focal radiation therapy, then underwent a matched, unrelated bone marrow transplant and continues in remission 37 months later. Review of the literature revealed 10 cases in other children younger than 21-years-old with AML and breast involvement. These cases are summarized, and potential pathophysiologic mechanisms of spread are discussed. Breast involvement in AML is rare in children. However, regular breast examinations should be performed as part of routine follow-up in all girls with AML.

A High-Resolution Microwave Study of the Conformations of Butan-2-ol in a Supersonic Expansion

The microwave Fourier transform spectrum of the chiral, secondary alcohol butan-2-ol has been recorded in the range 6-18 GHz. The spectrum is relatively dense, due to the large number of species formed in the supersonic expansion used. Three conformational isomers of the butan-2-ol molecule have been identified and their spectra assigned using a semirigid, asymmetric-rotor model. They correspond to the three configurations that the central C-C bond can adopt. The basis of our assignment is a series of ab initio calculations, which have been performed using the GAUSSIAN 94 package, good agreement being observed between theoretical and experimental values of the rotational constants. First-order centrifugal distortion coefficients have also been extracted. It has proven possible, by examination of the relative strengths of a-, b-, and c-type transitions, to infer some further information about the position of the hydroxyl hydrogen atom within each conformer. Copyright 2001 Academic Press.

Effects of diazepam on cognitive processes in normal subjects

The effects of 10 mg orally-administered diazepam on various aspects of cognition were examined in ten male subjects. Diazepam produced a subjective sense of cognitive impairment and impaired auditory vigilence, immediate recognition of twice presented words, and context-dependent free recall. There was a trend for a significant proportion of subjects to show impairment in delayed recognition of twice-presented words. There was no impairment of context-independent semantic memory, or of subjects' ability to judge how well they had performed on the free recall task. In fact, subjects' subjective sense of cognitive impairment was correlated with their performance on context-dependent memory tasks.