A process of making a stretch of consecutive amino acids comprising a C-terminal cysteine or a C-terminal selenocysteine, comprising: (a) transfecting a cell with a recombinant nucleic acid which comprises (i) a first portion, the sequence of which encodes a N-terminal signal sequence, contiguous with (ii) a second portion, the sequence of which encodes a stretch of consecutive amino acids selected from a Fc fragment of a human IgG immunoglobulin containing the M1 domain or a portion thereof, or the extracellular domain of human CD4, human TNR1A, human TNR1B, human VGFR1, human VGFR2, human VGFR3, human ErbB1, human ErbB2, human ErbB3 or human ErbB4, contiguous with (iii) a third portion, the sequence of which encodes a C-terminal intein-containing binding domain, under conditions permitting (i) synthesis of a chimeric polypeptide comprising the N-terminal signal sequence contiguous with the stretch of consecutive amino acids contiguous with the C-terminal intein-containing binding domain; and (ii) cleavage of the N-terminal signal sequence from the chimeric polypeptide, so as to produce a second chimeric polypeptide comprising the stretch of consecutive amino acids contiguous with the C-terminal intein-containing binding domain, (b) isolating the second chimeric polypeptide produced in step (a); (c) treating the second chimeric polypeptide so as to cause thio-mediated cleavage of the C-terminal intein-containing binding domain from the stretch of consecutive amino acids so as to form a C- terminal thioester; (d) ligating the product of step (c) with a cysteine residue or selenocysteine residue at its C- terminus so as to form a product with a C-terminal cysteine or a C-terminal selenocysteine; and (e) recovering the product of step (d) which is the stretch of consecutive amino acids comprising the C-terminal cysteine or the C-terminal selenocysteine. (a) transfecting a cell with a recombinant nucleic acid which comprises (i) a first portion, the sequence of which encodes a N-terminal signal sequence, contiguous with (ii) a second portion, the sequence of which encodes a stretch of consecutive amino acids selected from a Fc fragment of a human IgG immunoglobulin containing the M1 domain or a portion thereof, or the extracellular domain of human CD4, human TNR1A, human TNR1B, human VGFR1, human VGFR2, human VGFR3, human ErbB1, human ErbB2, human ErbB3 or human ErbB4, contiguous with (iii) a third portion, the sequence of which encodes a C-terminal intein-containing binding domain, under conditions permitting (i) synthesis of a chimeric polypeptide comprising the N-terminal signal sequence contiguous with the stretch of consecutive amino acids contiguous with the C-terminal intein-containing binding domain; and (ii) cleavage of the N-terminal signal sequence from the chimeric polypeptide, so as to produce a second chimeric polypeptide comprising the stretch of consecutive amino acids contiguous with the C-terminal intein-containing binding domain, (i) a first portion, the sequence of which encodes a N-terminal signal sequence, contiguous with (ii) a second portion, the sequence of which encodes a stretch of consecutive amino acids selected from a Fc fragment of a human IgG immunoglobulin containing the M1 domain or a portion thereof, or the extracellular domain of human CD4, human TNR1A, human TNR1B, human VGFR1, human VGFR2, human VGFR3, human ErbB1, human ErbB2, human ErbB3 or human ErbB4, contiguous with (iii) a third portion, the sequence of which encodes a C-terminal intein-containing binding domain, under conditions permitting (i) synthesis of a chimeric polypeptide comprising the N-terminal signal sequence contiguous with the stretch of consecutive amino acids contiguous with the C-terminal intein-containing binding domain; and (ii) cleavage of the N-terminal signal sequence from the chimeric polypeptide, so as to produce a second chimeric polypeptide comprising the stretch of consecutive amino acids contiguous with the C-terminal intein-containing binding domain, (i) synthesis of a chimeric polypeptide comprising the N-terminal signal sequence contiguous with the stretch of consecutive amino acids contiguous with the C-terminal intein-containing binding domain; and (ii) cleavage of the N-terminal signal sequence from the chimeric polypeptide, so as to produce a second chimeric polypeptide comprising the stretch of consecutive amino acids contiguous with the C-terminal intein-containing binding domain, (b) isolating the second chimeric polypeptide produced in step (a); (c) treating the second chimeric polypeptide so as to cause thio-mediated cleavage of the C-terminal intein-containing binding domain from the stretch of consecutive amino acids so as to form a C- terminal thioester; (d) ligating the product of step (c) with a cysteine residue or selenocysteine residue at its C- terminus so as to form a product with a C-terminal cysteine or a C-terminal selenocysteine; and (e) recovering the product of step (d) which is the stretch of consecutive amino acids comprising the C-terminal cysteine or the C-terminal selenocysteine.