No abstract

The Rh(I) and Rh(III) hydrides HRh(dppb)2 and [HRh(dppb)2(NCCH3)](BF4)2 (where dppb is 1,2-(bis(diphenylphosphino)benzene) have been prepared, and a structural study of [HRh(dppb)2(NCCH3)](BF4)2 has been completed. The latter complex is an octahedral complex with a trans arrangement of the hydride and acetonitrile ligands. A pK a value of 9.4 was measured for this complex by equilibration of [Rh(dppb)2](BF4) with 4-bromoanilinium tetrafluoroborate in acetonitrile. [Rh(dppb)2](BF4) reacts with H2 in the presence of Pt(dmpp)2, which acts as a base, to form HRh(dppb)2 and [HPt(dmpp)2](BF4) (where dmpp = 1,2-bis(dimethylphosphino)propane). An equilibrium constant of 0.42 ± 0.2 was measured for this reaction. Using this equilibrium measurement and a thermodynamic cycle, the hydride donor ability (ΔG°H-) of HRh(dppb)2 was determined to be 34 kcal/mol. This value indicates that HRh(diphosphine)2 complexes are powerful hydride donors. Similarly the pK a value of HRh(dppb)2 was calculated to be 35 from a thermodynamic cycle that included the potential of the Rh(I/−I) couple (E 1/2 = −2.02 V vs ferrocene). These results combined with results from the literature suggest the following order of hydricity for five-coordinate, 18-electron hydrides:  second row > third row > first row. Similarly an acidity order of second row ≥ first row > third row is deduced.

Competing interests M.R., S.G. hold patents related to CART22. C.H.J. has received grant support from Novartis, and has patents related to CAR therapy with royalties paid from Novartis to the University of Pennsylvania. C.H.J. is also a scientific founder and holds equity in Tmunity Therapeutics. S.A.G. has received support from Novartis, Servier and Kite, and serves as a consultant, member of the scientific advisory board or study steering committee for Novartis,

5-Methylcytosine (m5C) is a RNA modification that exists in tRNAs and rRNAs and was recently found in mRNAs. Although it has been suggested to regulate diverse biological functions, whether m5C RNA modification influences adult stem cell development remains undetermined. In this study, we show that Ypsilon schachtel (YPS), a homolog of human Y box binding protein 1 (YBX1), promotes germ line stem cell (GSC) maintenance, proliferation, and differentiation in the Drosophila ovary by preferentially binding to m5C-containing RNAs. YPS is genetically demonstrated to function intrinsically for GSC maintenance, proliferation, and progeny differentiation in the Drosophila ovary, and human YBX1 can functionally replace YPS to support normal GSC development. Highly conserved cold-shock domains (CSDs) of YPS and YBX1 preferentially bind to m5C RNA in vitro. Moreover, YPS also preferentially binds to m5C-containing RNAs, including mRNAs, in germ cells. The crystal structure of the YBX1 CSD-RNA complex reveals that both hydrophobic stacking and hydrogen bonds are critical for m5C binding. Overexpression of RNA-binding–defective YPS and YBX1 proteins disrupts GSC development. Taken together, our findings show that m5C RNA modification plays an important role in adult stem cell development.