in contrast , base analogs that have alterations that appear in the major groove of the dna helix , such as uracil , 5-bromouracil , 5-methylcytosine , 5-hydroxymethylcytosine , and [ 5-hgsr ] pyrimidines , do not prevent utilization of the promoter .
C0041917
uracil
C0006242
5-bromouracil