sentences:  Spacer peptide 1 (SP1, previously 'p2') is a 14-amino acid polypeptide intervening between CA and NC.Cleavage of the CA-SP1 junction is the final step in viral maturation, which allows CA to condense into the viral capsid.SP1 is unstructured in solution but, in the presence of less polar solvents or at high polypeptide concentrations, it adopts an α-helical structure.