The trimeric Cdk7±cyclin H±Mat1 complex comprises the kinase subunit of basal transcription factor TFIIH and has been shown to function as a cyclin-dependent kinase (Cdk)-activating kinase. Herein we report that disruption of the murine Mat1 gene leads to periimplantation lethality coincident with depletion of maternal Mat1 protein. In culture, Mat1 ±/± blastocysts gave rise to viable post-mitotic trophoblast giant cells while mitotic lineages failed to proliferate and survive. In contrast to wild-type trophoblast giant cells, Mat1 ±/± cells exhibited a rapid arrest in endoreduplication, which was characterized by an inability to enter S phase. Additionally, Mat1 ±/± cells exhibited defects in phosphorylation of the C-terminal domain (CTD) of RNA polymerase II on both Ser5 and Ser2 of the heptapeptide repeat. Despite this, Mat1 ±/± cells demonstrated apparent transcriptional and translational integrity. These data indicate an essential role for Mat1 in progression through the endocycle and suggest that while Mat1 modulates CTD phosphorylation, it does not appear to be essential for RNA polymerase II-mediated transcription.

Cell cycle progression is dependent on the sequential activity of cyclin‐dependent kinases (CDKs). For full activity, CDKs require an activating phosphorylation of a conserved residue (corresponding to Thr160 in human CDK2) carried out by the CDK‐activating kinase (CAK). Two distinct CAK kinases have been described: in budding yeast Saccharomyces cerevisiae, the Cak1/Civ1 kinase is responsible for CAK activity. In several other species including human, Xenopus, Drosophila and fission yeast Schizosaccharomyces pombe, CAK has been identified as a complex homologous to CDK7–cyclin H (Mcs6–Mcs2 in fission yeast). Here we identify the fission yeast Csk1 kinase as an in vivo activating kinase of the Mcs6–Mcs2 CAK defining Csk1 as a CAK‐activating kinase (CAKAK).

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The increasing availability of high-quality reference genomic sequences has created a demand for ways to survey the sequence differences present in individual genomes. Here we describe a DNA sequencing method based on hybridization of a universal panel of tiling probes. Millions of shotgun fragments are amplified in situ and subjected to sequential hybridization with short fluorescent probes. Long fragments of 200 bp facilitate unique placement even in large genomes. The sequencing chemistry is simple, enzyme-free and consumes only dilute solutions of the probes, resulting in reduced sequencing cost and substantially increased speed. A prototype instrument based on commonly available equipment was used to resequence the Bacteriophage lambda and Escherichia coli genomes to better than 99.93% accuracy with a raw throughput of 320 Mbp/day, albeit with a significant number of small gaps attributed to losses in sample preparation.