High efficiency of site-directed mutagenesis mediated by a single PCR product

Molecular imaging of glycogen synthase kinase-3beta and casein kinase-1alpha kinases

Glycogen synthase kinase-3beta (GSK3beta) and casein kinase-1alpha (CK1alpha) are multifunctional kinases that play critical roles in the regulation of a number of cellular processes. In spite of their importance, molecular imaging tools for noninvasive and real-time monitoring of their kinase activities have not been devised. Here we report development of the bioluminescent GSK3beta and CK1alpha reporter (BGCR) based on firefly luciferase complementation. Treatment of SW620 cells stably expressing the reporter with inhibitors of GSK3beta (SB415286 and LiCl) or CK1alpha (CKI-7) resulted in dose- and time-dependent increases in BGCR activity that were validated using Western blotting. No increase in bioluminescence was observed in the case of S37A mutant (GSK3beta inhibitors) or S45A mutant (CKI-7), demonstrating the specificity of the reporter. Imaging of mice tumor xenograft generated with BGCR-expressing SW620 cells following treatment with LiCl showed unique oscillations in GSK3beta activity that were corroborated by phosphorylated GSK3beta immunoblotting. Taken together, the BGCR is a novel molecular imaging tool that reveals unique insight into GSK3beta and CK1alpha kinase activities and may provide a powerful tool in experimental therapeutics for rapid optimization of dose and schedule of targeted therapies and for monitoring therapeutic response.

Antisense transcription controls cell fate in Saccharomyces cerevisiae

Entry into meiosis is a key developmental decision. We show here that meiotic entry in Saccharomyces cerevisiae is controlled by antisense-mediated regulation of IME4, a gene required for initiating meiosis. In MAT a/alpha diploids the antisense IME4 transcript is repressed by binding of the a1/alpha2 heterodimer at a conserved site located downstream of the IME4 coding sequence. MAT a/alpha diploids that produce IME4 antisense transcript have diminished sense transcription and fail to initiate meiosis. Haploids that produce the sense transcript have diminished antisense transcription and manifest several diploid phenotypes. Our data are consistent with transcription interference as a regulatory mechanism at the IME4 locus that determines cell fate.

Identification of domains mediating transcriptional activation and cytoplasmic export in the caudal homeobox protein Cdx-3

The caudal genes have important functions in embryonic development and cell differentiation. The caudal-related protein Cdx-2/3 (the protein designated Cdx-2 in the mouse and Cdx-3 in the hamster) is expressed in the gastrointestinal epithelium and in islet and enteroendocrine cells, where it activates proglucagon gene transcription. We show here that Cdx-3 sequences amino-terminal to the homeodomain (amino acids 1-180) function as a heterologous transcriptional activation domain when fused to the LexA DNA binding domain. A Cdx-3-Pit-1 fusion protein containing only the first 83 amino acids of Cdx-3 linked to the POU domain of Pit-1 markedly stimulated the transcriptional activity of a Pit-1-responsive promoter. Analysis of the transcriptional properties of Cdx-3 mutants in fibroblasts and islet cells revealed distinct amino-terminal subdomains that function in a cell-specific manner. Point mutations within the amino-terminal A domain were associated with reduced transcriptional activity. Furthermore, internal deletions and selected point mutations within domain A, but not the B or C domains, resulted in accumulation of mutant Cdx-3 in the cytoplasm. Unexpectedly, mutation of an Asp-Lys-Asp motif within domain A identified a putative cytoplasmic membrane-associated export signal that mediates Cdx-3 compartmentalization. These experiments delineate unique activities for specific amino-terminal sequences that are functionally important for Cdx-3 biological activity.

An efficient system for site-directed mutagenesis to make various mutants of the env gene of human immunodeficiency virus type 1

We developed an efficient system of site-directed mutagenesis for the envelope (env) gene of human immunodeficiency virus type 1 (HIV-1). To make a template plasmid for mutagenesis, pS+B/MluI, two independent selection markers, i.e. a unique restriction site, MluI, and an in-frame termination codon, were introduced into the region encoding the V3 domain of the env gene of an HIV-1 strain, NL4-3, which had been cloned in the pUC118 plasmid. When the env gene of the pS+B/MluI plasmid was mutated successfully using mutagenic primers such as synthetic oligonucleotides or PCR-amplified DNA fragments longer than 1.5 kbp, the plasmids became resistant to digestion with MluI and competent env genes were formed by suppression of the in-frame termination. Various site-directed mutants of the env gene of HIV-1 were accurately constructed in a short time even in the absence of proper restriction sites by this system. The system of site-directed mutagenesis we reported here will be a useful method to analyze the functions of variable genes like the env gene of HIV-1 precisely and rapidly.