In Brief

Technology

A high signal-to-noise Ca²⁺ probe composed of a single green fluorescent protein. Nakai, J., Ohkura, M. & Imoto, K. Nature Biotechnol. 19 , 137?141 (2001) [PubMed]

Currently available Ca²⁺ probes based on green fluorescent protein (GFP) have a low signal-to-noise ratio, limiting their use. Nagai et al. have built a GFP with a Ca²⁺?calmodulin-sensitive enzyme tagged on one end and calmodulin on the other. Ca²⁺-induced conformational changes cause a large increase in fluorescence.

Cell signalling

Regulation of a novel human phospholipase C, PLC-ɛ, through membrane targeting by Ras. Song, C. et al. J. Biol. Chem. 276, 2752?2757 (2001) [PubMed]

A novel bifunctional phospholipase C that is regulated by Gα12 and stimulates the Ras/MAP kinase pathway. Lopez, I. et al. J. Biol. Chem. 276, 2758?2765 (2001) [PubMed]

Phospholipase Cɛ: a novel Ras effector. Kelley, G. G. et al. EMBO J. 20, 743?754 (2001) [Contents page]

These papers report a new mammalian phospholipase C that is activated by Ras (as well as the α-subunit of a heterotrimeric G protein) but can also activate Ras through its guanine nucleotide exchange factor domain.

DNA recombination

Branch migration and Holliday junction resolution catalyzed by activities from mammalian cells. Constantinou, A., Davies, A. A. & West, S. C. Cell 104, 259?268 (2001) [Contents]

A key intermediate of homologous recombination and double-stranded-break repair is the Holliday junction. This dynamic structure can move (branch migrate) to generate stretches of heteroduplex DNA, and it is resolved by a junction-specific endonuclease. These reactions are well characterized in bacteria, and West and colleagues now describe analogous activities in mammalian cell-free extracts. This report highlights the conservation of this pathway from prokaryotes to mammals.

DNA repair

XRCC1 stimulates human polynucleotide kinase activity at damaged DNA termini and accelerates DNA single-strand break repair. Whitehouse, C. J. et al. Cell 104, 107?117 (2001) [Contents page]

XRCC1 is involved in repairing single-stranded DNA breaks, but little is known about its biochemical function. Now, using XRCC1 as bait in a yeast two-hybrid screen, the authors have identified a new partner for it ? human polynucleotide kinase (PNK). XRCC1 stimulates the DNA kinase and phosphatase activities of PNK at damaged DNA termini, and this accelerates the repair reaction. It is, claim the authors, ?a novel pathway for mammalian single-strand break repair?.