Octamer and SPH motifs in the U1 enhancer cooperate to activate U1 RNA gene expression.

Abstract

The transcriptional enhancer of a chicken Ul small nuclear RNA gene has been shown to extend over approximately 50 base pairs of DNA sequence located 180 to 230 base pairs upstream of the Ul transcription initiation site. It is composed of multiple functional motifs, including a GC box, an octamer motif, and a novel SPH motif. The contributions of these three distinct sequence motifs to enhancer function were studied with an oocyte expression assay. Under noncompetitive conditions in oocytes, the SPH motif is capable of stimulating Ul RNA transcription in the absence of the other functional motifs, whereas the octamer motif by itself lacks this ability. However, to form a transcription complex that is stable to challenge by a second competing small nuclear RNA transcription unit, both the octamer and SPH motifs are required. The GC box, although required for full enhancer activity, is not essential for stable complex formation in oocytes. Site-directed mutagenesis was used to study the DNA sequence requirements of the SPH motif. Functional activity of the SPH motif is spread throughout a 24-base-pair region 3' of the octamer but is particularly dependent upon sequences near an SphI restriction site located at the center of the SPH motif. Using embryonic chicken tissue as a source material, we identified and partially purified a factor, termed SBF, that binds sequence specifically to the SPH motif of the Ul enhancer. The ability of this factor to recognize and bind to mutant enhancer DNA fragments in vitro correlates with the functional activity of the corresponding enhancer sequences in vivo.The small nuclear RNAs (snRNAs) of the U family are evolutionarily conserved and metabolically stable RNA molecules present in the nuclei of eucaryotic cells. Considerable evidence exists that the Ul, U2, U4, U5, and U6 snRNAs are involved in the splicing of mRNA precursors (37). With the exception of U6, the snRNAs are synthesized by RNA polymerase II (6) and have a distinctive N2,N2,N7-trimethylguanosine cap structure (34).The genes that code for the vertebrate snRNAs are usually present in multiple copies per genome and have several features that distinguish them from protein-coding genes. The promoter regions of snRNA genes lack transcription signals normally found upstream of genes transcribed by RNA polymerase II (e.g., they lack TATA and CCAAT boxes). Nevertheless, they contain two distinct and evolutionarily conserved cis-acting regulatory regions within their 5'-flanking DNA sequences that are important for snRNA gene expression: a proximal region centered near position -55 relative to the transcription initiation site and a distal region located near position -200 (reviewed in references 6 and 32). Moreover, the formation of the 3' ends of the snRNAs is dependent on the initiation of transcription from an snRNA gene promoter (4,13,14,28). Because of the unique properties of snRNA transcription complexes, the promoter elements of snRNA genes are not functionally interchangeable with comparable elements of mRNA genes...

Changes in UsnRNA biosynthesis during rat liver regeneration

“…Several cis acting elements (e.g Sph motiff, Octamer motiff, GC box, LINES sequence etc.) similar to that of mRNA genes have been characterised in different UsnRNAs along with some transacting factors [46]. It is quite evident that these cis-acting elements have some role in cellular proliferation, differentiation as well as tissue specific gene expression [47].…”

“…It is quite evident that these cis-acting elements have some role in cellular proliferation, differentiation as well as tissue specific gene expression [47]. Besides, it has been shown that these UsnRNA enhancer elements can act in a variety of cis-linked configurations to activate gene transcription synergistically [46]. Thus, the differential regulation of these UsnRNAs' transcription during the proliferative phase of liver regeneration might be controlled by all these elements.…”

The ubiquitous transcription factor Oct-1 and the liver-specific factor HNF-1 are both required to activate transcription of a hepatitis B virus promoter.

“…These findings are unexpected in that Oct-1 has so far been implicated only in transcription of housekeeping genes. However, even for at least some of the housekeeping genes, Oct-1 is incapable of activating transcription in the absence of other ubiquitous factors that bind to other cis elements in these promoters (2,33,42). The transcription factor Spl has been implicated as one of these factors (2), but the other factors are as yet uncharacterized.…”

Functional characterization of elements in a human U6 small nuclear RNA gene distal control region.

“…6, -OCT (12). Another control element, the SPH motif, has been identified within the distal regions of several vertebrate snRNA genes (7,35,36,50) and the Xenopus tRNA(Ser)Sec 5' flanking region (32). However, the extended NONOCT sequence has a very poor fit to these snRNA gene SPH motifs, and therefore we consider it unlikely that the same transcription factor interacts with these control elements.…”

“…Many Pol II-transcribed snRNA gene distal regions have been dissected and found to be composed of an octamer element and a second sequence element in close proximity. Some of the second sequence elements that have been identified include Spl binding sites (2,14,45), SPH motifs (7,35,36,50), an AP-2 binding site (48), a cyclic AMP (cAMP) response element (48), and a CCAAT motif (1,38). In the case of the human U2 snRNA distal region, Oct-1 protein and Spl may interact (15).…”