A series of analogues of S‐adenosylmethionine (SAM) have been used to examine the molecular‐recognition characteristics of an RNA genetic element or riboswitch. Biochemical assays indicate that the riboswitch of the SAM‐I class is highly selective for SAM and exhibits a pattern of molecular recognition that is distinct from that of the SAM‐II class of riboswitches.

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IUFI is a pancreatic fi ceil-specific factor which binds to the sequence 5'-CPyCTAATG-3' (CT box) within the human insulin gene enhancer. Here we show that IWFI is composed of 2 binding activities that can be separated by DEAE ion exchange chromatography. South Western blot analysis indicates that these distinct binding activities have apparent molecular weights of ii5 kDa and 46 kDa.

Electrophoretic mobility shift assays were performed using oligonucleotides corresponding to known protein binding sites within the human insulin gene enhancer and nuclear extracts from mouse pancreatic a and /I cell lines. The results demonstrate that a previously described factor, IUF-1, binds to three sites at -82 (the CT1 box), -215 (the CT2 box), and -319 (the CT3 box) in the human insulin gene enhancer. ILJF-1 was present only ing but not in a cells, while all other DNA-binding proteins were present in both cell lines. IUF-1 may therefore be an important determinant of insulin gene /I cell-specific expression. In the human insulin gene the promoter-proximal E box (IEBl/NIR) is conserved, and binds a factor with similar properties to IEF-1 [16]. The distal E box (IEB2/ FAR) is not conserved in the human insulin gene, however this region is transc~ptionally important [ 17j and has been identified as a binding site for the ubiquitous HLH protein USE; [16]. The human insulin gene contains TAAT box elements at -82 {the CT-1 box), -215 (the CT-2 box) and at -319 (the CT-3 box). The CT-2 box binds a factor called IUF-1 [ 181. The human insulin gene also contains a powerful negative regulatory element (NRE) at -270, and several other protein binding sites including the GGl/GG2 motifs at -145 to -130, a CAMP response element (CRE) at -183 to -176, an SPl site at -346 to -341, and an enhancer core sequence at -314 to -306 [17].The mouse pancreatic cell lines, aTCI and flC3, were derived from transgenic mice expressing the SV40 large T antigen under the control of either the glucagon or insulin enhancer/promoter, respectively [19,20]. Tissue-specific expression of the transgene led to the formation of either glucagonomas or insulinomas, from which immortalised cell lines were established. aTC1 and /ITC3 cells produce greater quantities of glucagon or of insulin than other islet cell lines. In addition, they may be closer to terminally differentiated cells than other islet cell lines, such as HIT T15 and RIN m5F