Recent development of molecular genetic techniques are rapidly advancing understanding of the functional role of brain circuits in behavior. Critical to this approach is the ability to target specific neuron populations and circuits. The collection of over 250 BAC Cre-recombinase driver lines produced by the GENSAT project provides a resource for such studies. Here we provide characterization o...

Functional analysis of mammalian genes relies, in part, on targeted mutations generated by homologous recombination in mice. We have developed a strategy for adipose-specific inactivation of loxP-floxed gene segments. Transgenic mice have been established that express Cre recombinase under the control of the adipose-specific aP2 enhancer/promoter. Crossing of the aP2/ Cre mice with any loxP-flo...

Human RNase H1 cleaves RNA only when the RNA is present in a DNA-RNA heteroduplex. Previous efforts to create RNase H1 knockout mice resulted in embryonic lethality1, but demonstrated that RNase H1 is required for mitochondrial function. We constructed viable constitutive hepatocyte liver specific RNase H1 knock out mice by coupling the Cre recombinase to an albumin promoter as albumin is not e...

The activity of a fourth conserved tyrosine site-specific recombinase (Tsr) of Bacteroides fragilis was characterized. Its gene, tsr19, is adjacent to mpi, encoding the global DNA invertase regulating capsular polysaccharide biosynthesis. Unlike the other described Tsrs of B. fragilis, Tsr19 brings about inversion of two DNA regions, one local and one located distantly.

Site-specific recombinase systems (Cre-loxP, Flp-FRT, and phi C31-att) are transforming both forward and reverse genetics in mice. By enabling high-fidelity DNA modifications to be induced in vitro or in vivo, these systems have incited a wave of new biology, advancing our understanding of gene function, genetic relationships, development, and disease.

Generation of a diverse repertoire of antigen receptor specificities via DNA recombination underpins adaptive immunity. In this issue ofGenes&Development, Carmona and colleagues (pp. 909-917) provide novel insights into the origin and function of recombination-activating gene 1 (RAG1) and RAG2, the lymphocyte-specific components of the recombinase involved in the process.