To activate transcription of the g/nA gene, the dimeric NTRC protein (_nitrogen regulatory protein C) of enteric bacteria binds to an enhancer located -100 bp upstream of the promoter. The enhancer is composed of two binding sites for NTRC that are three turns of the DNA helix apart. One role of the enhancer is to tether NTRC in high local concentration near the promoter to allow for its frequent interaction with r s4 holoenzyme by DNA looping. We have found that a second role of the enhancer is to ensure oligomerization of NTRC into a complex of at least two dimers that is required for transcriptional activation. Formation of this complex is greatly facilitated by a protein-protein interaction between NTRC dimers that is increased when the protein is phosphorylated.

Recombination, or chimera formation, is known to occur between related template sequences present in a single PCR amplification. To characterize the conditions under which such recombinant amplification products form we monitored the exchange of sequence between two homologous templates carrying different restriction sites separated by 282 bp. Using a typical cycling program the rates of recombination between the two restriction sites were 1 and 7% using Taq and Vent polymerases respectively over 12 doublings. However, by using long elongation times and cycling only to the mid-point of the amplification recombination could be suppressed below visual detection with both polymerases. Conversely, cycling programs designed to promote incomplete primer elongation and subsequent template strand exchange stimulated recombination to >20%.

IL-10 is a unique cytokine because it is anti-inflammatory and immunosuppressive. IL-10 is regulated at the level of transcription, but the critical motifs and the relevant transcription factors controlling this gene have remained elusive to date. We now report that a sequence at −120 bp in the human IL-10 promoter binds Stat3 but no other Stat proteins. Mutation of this motif abrogates LPS-induced trans-activation. Overexpression of dominant negative Stat3 suppresses promoter activity, while wild-type Stat3 leads to an enhancement of this activity. Our results show that Stat3, by binding to a single motif in the IL-10 promoter, is controlling expression of the human IL-10 gene.

NTRC is a prokaryotic enhancer-binding protein that activates transcription by ¢rS4-holoenzyme. NTRC has an ATPase activity that is required for transcriptional activation, specifically for isomerization of closed complexes between ¢rS4-holoenzyme and a promoter to open complexes. In the absence of ATP hydrolysis, there is known to be a kinetic barrier to open complex formation (i.e., the reaction proceeds so slowly that the polymerase synthesizes essentially no transcripts even from a supercoiled template). We show here that open complex formation is also thermodynamically unfavorable. In the absence of ATP hydrolysis the position of equilibrium between closed and open complexes favors the closed ones. Use of linear templates with a region of heteroduplex around the transcriptional start site--"preopened" templates--does not bypass the requirement for either NTRC or ATP hydrolysis, providing evidence that the rate-limiting step in open complex formation does not lie in DNA strand denaturation per se. These results are in contrast to recent findings regarding the ATP requirement for initiation of transcription by eukaryotic RNA polymerase II; in the latter case, the ATP requirement is circumvented by use of a supercoiled plasmid template or a preopened linear template.

We have isolated and characterized both cDNA and genomic DNA of the mouse lysozyme M gene. Derivation of the amino acid sequence from the nucleotide sequences revealed six positions in the carboxyl terminus that differ from partial sequences previously published. The differential detection of specific mRNAs from the closely related lysozyme M and P genes has revealed different but overlapping tissue specificities of expression. The M gene is expressed weakly in myeloblasts, moderately in immature macrophages, and strongly in both mature macrophages and macrophagerich tissues, while high levels of P transcripts are present only in small intestine. Sites of protein accumulation, rather than gene expression, have been identified by comparative quantitation of mRNA and enzyme levels.Since the discovery in 1922 of lysozyme (EC 3.2