Background of the antigen
SAP 155 is a 1,304 amino acid member of the SF3B1 family and contains eleven HEAT repeats. Localized to nuclear speckles and also to the cytoplasm during mitosis, SAP 155 is a subunit of the SF3B splicing factor. The SF3B splicing factor is a U2 snRNP-associated protein complex essential for spliceosome assembly. SF3B contains the spliceosomal proteins SAP 49, SAP 130, SAP 145 and SAP 155. Concomitant with splicing catalysis, SAP 155 is phosphorylated at its N-terminal Thr-Pro dipeptide motifs by Dyrk1A and cyclin E/Cdk2. This modification of SAP 155 is vital for a functional spliceosome as it is an essential event in the basic splicing reaction. Due to alternative splicing events, various SAP 155 isoforms are produced.