Transcription start-site mapping.

he synthesis of proteins is an essential process in cell growth and cell proliferation. The DNA sequence of a gene is first copied (transcribed) into an RNA sequence that is translated into a particular amino acid sequence. One strand of the gene, the RNA-like strand (or sense strand) has a nucleotide sequence equivalent to that of the RNA transcript (mRNA) with thymine replacing uracil. The complementary strand is often termed the template strand (or antisense strand), reflecting its role in the transcription process. Transcription takes place starting from the 5'-end and proceeding toward the 3'-end of the RNA product. The transcription process is usually described in three stages, namely, initiation, chain elongation, and termination. This chapter focuses on the initiation of transcription.