vector may be derived from plasmid or viral dna a number of suitable expression vectors for expression in the host cells mentioned herein are commercially available or described in the literature the recombinant vector may further comprise a dna sequence enabling the vector to replicate in the host cell in question an example of such a sequence when the host cell is a mammalian cell is the sv40 origin of replication the vector may also comprise a selectable marker e g a gene whose product complements a defect in the host cell such as the gene coding for dihydrofolate reductase dhfr or one which confers resistance to a drug e g ampicillin kanamycin tetracycline chloramphenicol neomycin hygromycin or methotrexate the vector may also comprise an amplifiable gene such as dhfr such that cells having multiple copies of the amplifiable gene and flanking sequences including the mutant fsh dna can be selected for on appropriate media the term u201c control sequences u201d is defined herein to include all components which are necessary or advantageous for the expression of the polypeptide of the invention examples of suitable control sequences for directing transcription in mammalian cells include the early and late promoters of sv40 and adenovirus e g the adenovirus 2 major late promoter the mt 1 metallothionein gene promoter and the human cytomegalovirus immediate early gene promoter.