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Numerous genes contain TATAA-less promoters, and the control of transcriptional initiation in this important promoter class is not understood. We have determined that protein-DNA interactions at three of the four proximal GC box sequence elements in one such promoter, that of the hamster dihydrofolate reductase gene, control initiation and relative use of the major and minor start sites. Our results indicate that although the GC boxes are apparently equivalent with respect to factor binding, they are not equivalent with respect to function. At least two properly positioned GC boxes were required for initiation of transcription. Abolishment of DNA-protein interaction by site-specific mutation of the most proximal GC box (box I) resulted in a fivefold decrease in transcription from the major initiation site and a threefold increase in heterogeneous transcripts initiating from the vicinity of the minor start site in vitro and in vivo. Mutations that separately abolished interactions at GC boxes II and III while leaving GC box I intact affected the relative utilization of both the major and minor initiation sites as well as transcriptional efficiency of the promoter template in in vitro transcription and transient expression assays. Interaction at GC box IV when the three proximal boxes were in a wild-type configuration had no effect on transcription of the dihydrofolate reductase gene promoter. Thus, GC box interactions not only are required for efficient transcription but also regulate start site utilization in this TATAA-less promoter.Transcription of eucaryotic promoters by RNA polymerase II involves multiple sequence elements and protein factors that associate with these sequences. Certain DNAprotein interactions regulate the efficiency of transcriptional initiation, while others have the additional role of specifying the transcriptional initiation site. In many class II gene promoters, a TATAA sequence element is located approximately 25 to 30 bp upstream of the transcription start site (5, 17); interaction of a factor(s) with this sequence specifies the site of initiation in many of these promoters (24, 41). However, in other eucaryotic promoters (7,25,47), interaction with TATAA appears not to specify the start site but rather to control the efficiency of transcription from a downstream initiation site. Another common important control element, CCAAT, is the target of factors that regulate the efficiency of transcription (13,24).A large subclass of polymerase II promoters lacks both TATAA and CCAAT sequence motifs but contains multiple GC boxes. This promoter class includes several housekeeping genes (e.g., the genes encoding dihydrofolate reductase [DHFR] (26), GCF-1 (27), and AP2 (35) have also been shown to interact with GC boxes. Determining the functional role of multiple GC boxes in the absence of TATAA and CCAAT motifs is crucial to the understanding of transcriptional regulation of this important class of promoters.It has been shown that GC boxes are required for efficient promoter activity in the...

Leptin inhibits food intake and increases metabolic rates in adult mice. Neonatal mice need to maximize food intake and also maintain high thermoregulatory metabolic rates to optimize survival, suggesting that leptin may function differentially in neonatal versus adult animals. The efficacy of exogenous leptin to alter these two physiological functions during development was thus examined in C57BL/6J lean (+/+ or ob/+) and ob/ ob(leptin-deficient) mice. Intraperitoneal leptin administration (1 mg/kg body wt) to lean and ob/ obpups from 7 to 10 days of age did not affect milk intake, oxygen consumption, body weight, or epididymal fat pad weights. Intracerebroventricular injection of 1 μg leptin to 9-day-old pups also failed to influence milk intake or oxygen consumption. Because neither lean nor ob/ obpups responded to exogenous leptin, high endogenous plasma leptin concentrations per se in these lean mice do not explain their resistance to leptin. Leptin administered intracerebroventricularly also failed to alter milk/food intakes of 17-day-old pups but markedly increased oxygen consumption of these older mice. By 28 days of age, intracerebroventricular leptin inhibited food intake. The well-defined actions of leptin to reduce food intake and enhance metabolic rates do not develop synchronously. The ability of leptin to accelerate metabolic rates is acquired early in life and independent of its anorectic action, which may promote survival of neonates.

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