Abstract
We provide here a protocol for the preparation of cap-analysis gene expression (CAGE) libraries, which allows for measuring the expression of eukaryotic capped RNAs and simultaneously map the promoter regions. The presented protocol simplifies the previously published ones and moreover produces tags that are 27 nucleotides long, which facilitates mapping to the genome. The protocol takes less than 5 days to complete and presents a notable improvement compared to previously published versions.