Any process involved in the selection of the specific location within the template strand of a DNA-dependent RNA polymerase promoter for hybridization of the cognate ribonucleotides and formation of first phosphodiester bond within the nascent transcript. [ http://www.ncbi.nlm.nih.gov/pubmed/18846104 http://www.ncbi.nlm.nih.gov/pubmed/16826228 ]