M. Jeffers et A. Pellicer, IDENTIFICATION OF MULTIPLE PROMOTERS WITHIN THE N-RAS PROTOONCOGENE, Biochimica et biophysica acta, N. Gene structure and expression, 1219(3), 1994, pp. 623-635
N-ras possesses a 'housekeeping' promoter, being G + C-rich and devoid
of a TATA-box. Transcription initiates at a number of locations withi
n this gene, a phenomena that is generally attributed to the absence o
f a TATA-box. In this report we investigate the possibility that multi
ple promoters, which could potentially contribute to the observed 5' e
nd heterogeneity, exist within the murine N-ras gene. The 5' region of
the gene was subdivided into several fragments, each corresponding to
a region in which one or more transcription initiation site(s) had be
en mapped, and the ability of each fragment to express a reporter gene
was assessed. Promoter activity was found associated with three indep
endent, non-overlapping fragments, two of which were located entirely
within transcribed regions of the gene. We found that these intragenic
promoters were able to express the N-ras gene itself, as well as the
reporter gene. In addition, we found that the activity of an intrageni
c promoter fragment was dependent upon the presence of regions encompa
ssing initiation sites, and that a small fragment (similar to 40 bp) e
ncompassing several initiation sites possessed promoter activity. Thes
e data support the existence of an 'initiator' element within the N-ra
s gene. Overall, our results demonstrate that multiple promoters resid
e within N-ras and suggest that they may play a role in generating the
observed mRNA 5' end heterogeneity. The identification of multiple pr
omoters within N-ras may have important implications regarding the reg
ulation of expression of this gene in normal and malignant tissues. In
addition, since a number of other genes with housekeeping promoters a
lso initiate transcription at multiple locations, it is possible that
the utilization of multiple promoters may represent a common feature o
f this class of genes.