The opening of specific segments of DNA is required for most types of genetic readout, including σ70‐dependent transcription. To learn how this occurs, a series of single point mutations were introduced into σ70 region 2. These were assayed for duplex DNA binding, DNA opening and DNA double strand–single strand fork junction binding. Band shift assays for closed complex formation implicated a series of arginine and aromatic residues within a minimal 26 amino acid region. Permanganate assays implicated two additional aromatic residues in DNA opening, known to form a parallel stack of the type that can accept a flipped‐out base. Substitution for either of these aromatics had no effect on duplex probe recognition. However, when a single unpaired −11 nucleotide is added to the probe, the mutants fail to bind appropriately to give heparin resistance. A model for DNA opening is presented in which duplex recognition by regions 2.3, 2.4 and 2.5 of sigma positions the pair of aromatic amino acids, which then create the fork junction required for stable opening.

The bacterial TATAAT ؊10 region sequence was the first promoter element to be identified, but how it functions is still not clear. Because the duplex element is melted during initiation, the effects of substitutions were studied in both single-and double-strand contexts. Band-shift results were particularly unexpected in the context of melted DNA. The effect of the lac UV5-melted ؊10 region on polymerase binding was found to include a large sequence nonspecific contribution. Instead the dominant role of single-stranded ؊10 region nucleotides was in directing the isomerization of the RNA polymerase to its heparin resistant form. This role becomes minimal when the melting is extended beyond the ؊10 region to encompass the transcription start site, as in the final open complex. The duplex binding results are in agreement with previous reports that showed positions ؊12T and ؊11A are of primary importance for promoter recognition. Thus the consensus ؊10 region sequences function in two ways, both before full promoter melting. They stabilize initial polymerase binding via duplex interactions and subsequently as single-stranded DNA they promote enzyme isomerization to the functional form.

Tran N, Valentín-Blasini L, Blount BC, McCuistion CG, Fenton MS, Gin E, Salem A, Hershman JM. Thyroid-stimulating hormone increases active transport of perchlorate into thyroid cells.

Sunitinib appears to target the cytosolic MEK/ERK and SAPK/JNK pathways in the RET/PTC1 cell lines, suggesting that blocking these pathways is at least part of the mechanism by which sunitinib inhibits cell proliferation and causes stimulation of NIS gene expression in RET/PTC1 cells.

The data indicate that sunitinib is unlikely to cause hypothyroidism by inhibition of iodide uptake.

A panel of seven ؊10 region DNA mutants was tested for holoenzyme binding against a panel of 13 region 2 mutants of 70. No patterns were noticed that would indicate unique interactions between individual amino acids and individual ؊10 region bases. Instead, certain amino acid substitutions led to increased holoenzyme binding to DNA, implying that the wild type interactions are associated with an inhibitory component. These inhibitory interactions were stronger on DNA containing non-consensus sequences, like those of typical promoters. In addition, the DNA segment downstream from the ؊10 element was also inhibitory to binding when in duplex form but stimulated binding when in single strand form. Overall, the data suggest that ؊10 region duplex recognition and melting have a large component of overcoming unfavorable protein:DNA base interactions, particularly when the bases are non-consensus, and that this contributes to setting physiologically appropriate variations in transcription rate.Escherichia coli gene transcription is accomplished by multisubunit RNA polymerase holoenzymes, with the 70 form being most common. 70 promoters typically contain two moderately conserved sequence elements separated by an optimal spacer length of 17 bp (1, 2). Naturally occurring promoters diverge from the consensus sequences to varying degrees, and these variations are required to obtain physiologically appropriate transcription rates. Other nearby DNA sequences also contribute to promoter activity (3, 4).The role of the Ϫ10 element is complex as it is recognized initially as duplex DNA and continues to function after the DNA is opened. The dominant function is associated with the non-template strand (5) and particularly with the Ϫ12 and Ϫ11 fork junction nucleotides at the boundary between duplex and non-template single strand DNA (6). The structure of holoenzyme bound to fork junction DNA (a duplex with a single strand tail from Ϫ11 to Ϫ7) is available (7). Protein:DNA contacts are not visible, but it is clear that certain amino acids in region 2 of 70 are close enough to the non-template single strand to make contact. There is no structure with Ϫ10 duplex DNA, so information about Ϫ10 duplex recognition comes solely from biochemical studies.In addition to marking promoters for recognition, the Ϫ10 element contributes to the rate of open complex formation, and this is known to proceed through binding and isomerization steps (8,9). The open complex pathway includes several intermediates in which the conformational state of the DNA and polymerase varies (10 -12). The final functional state is characterized by the resistance of the isomerized holoenzyme to the polyanionic inhibitor heparin (13). This isomerization of the enzyme can be measured independently of the opening of the DNA by using fork junction probes in which the DNA is premelted (14, 15). Such studies have indicated that the Ϫ10 region consensus bases have a critical role in enzyme isomerization (15). The bases also play a role in duplex recognition but have a lesser...

Abasic substitutions in the non-template strand and promoter sequence changes were made to assess the roles of various promoter features in sigma70 holoenzyme interactions with fork junction probes. Removal of -10 element non-template single strand bases, leaving the phosphodiester backbone intact, did not interfere with binding. In contrast these abasic probes were deficient in promoting holoenzyme isomerization to the heparin resistant conformation. Thus, it appears that the melted -10 region interaction has two components, an initial enzyme binding primarily to the phosphodiester backbone and a base dependent isomerization of the bound enzyme. In contrast various upstream elements cooperate primarily to stimulate binding. Features and positions most important for these effects are identified.

These data demonstrate that CREM expression is increased in thyroid cancer tissue and may play a role in the downregulation of NIS expression in thyroid cancer acting at the transcriptional level.