Patent ID: 8309071

Claim:
A nucleic acid comprising a foamy viral envelope gene encoding a modified foamy viral envelope polypeptide comprising a leader peptide (LP), a surface unit (SU) and a transmembrane domain (TM), wherein the polypeptide has an N terminus, wherein the nucleic acid is expression-optimized, wherein the nucleic acid encodes a modified foamy viral envelope gene comprising at least one mutation in a nucleic acid sequence encoding the LP, wherein the mutation results in inactivation of at least one ubiquitination site in the modified envelope polypeptide, and, wherein the foamy viral envelope gene comprises a sequence selected from the group consisting of SEQ ID NO: 7 (PE01), SEQ ID NO: 8 (PE02), SEQ ID NO: 9 (PE03), SEQ ID NO: 10 (SE01), SEQ ID NO: 11 (SE02) and SEQ ID NO: 12 (SE03).