Autophagy

The role of autophagy during the early neonatal starvation period. Kuma, A. et al. Nature 3 Nov 2004 (doi:10.1038/nature03029)

After birth, neonates face starvation until they can obtain nutrients from milk, so how do they survive this period? This paper shows that the level of autophagy in mice is upregulated in various tissues straight after birth. Mice deficient in a gene that is essential for autophagosome formation die within a day of birth and show reduced amino-acid concentrations in plasma and tissues. So, neonates seem to survive by producing amino acids through the autophagic degradation of 'self' proteins.

Microrna

Processing of primary microRNAs by the Microprocessor complex. Denli, A. M. et al. Nature 7 Nov 2004 (doi:10.1038/nature03049)

The Microprocessor complex mediates the genesis of microRNAs. Gregory, R. I. et al. Nature 7 Nov 2004 (doi:10.1038/nature03120)

Micro (mi)RNA processing involves two steps: primary miRNA transcripts (pri-miRNAs) are first cleaved into shorter, precursor miRNAs (pre-miRNAs) by an enzyme known as Drosha; and they are subsequently processed by another enzyme, Dicer, into ∼22-nt miRNAs. Two papers now report the existence of a Drosha-containing complex in humans and Drosophila melanogaster, which was named Microprocessor. Denli et al. identified a double-stranded RNA-binding protein — Pasha — in the D. melanogaster Microprocessor complex, which is required for pri-miRNA processing and for repression of miRNA-mediated genes. Gregory et al. identified two Drosha-containing complexes in human cells, of which the smaller one — Microprocessor — contained the double-stranded RNA-binding protein DGCR8, which is deleted in DiGeorge syndrome. Of the two complexes, only the Microprocessor complex seems to be required for miRNA processing.

Cytoskeleton

Formin is a processive motor that requires profilin to accelerate actin assembly and associated ATP hydrolysis. Romero, S. et al. Cell 119, 419–429 (2004)

The authors showed that the rapid, processive growth of actin filaments that is mediated by formins requires the nucleation enhancer profilin to be bound to actin–ATP, and for this profilin–actin complex to associate with the formin homology (FH) domains 1 and 2 of formin. FH1–FH2 accelerates the hydrolysis of ATP that is coupled to profilin–actin polymerization, and the free energy that is derived from this increases the rate constant for the binding of profilin–actin to barbed filament ends.