What are the properties of the SIRV transcripts’ terminal sequences?

The SIRVs as well as the ERCCs are in vitro transcription products, and therefore all RNAs start with a 5' ppp-G. Hence, cap-specific cDNA preparation methods are not feasible. The 3' end of each SIRV RNA is polyadenylated (SIRV isoforms and long SIRVs with 30 adenosines, ERCCs with 24 ± 1.05 nt adenosines), enabling oligo(dT) based selection and priming. The SIRVs User Guide contains a graphic representation of the SIRV design.
You can download the SIRV sequences and reference annotation files from the Lexogen web site at the following location: https://www.lexogen.com/sirvs/download/.