An isolated extended recombinant polypeptide (XTEN) comprising more than 100 to 3000 amino acid residues, wherein XTEN is characterized in that: (a) at least 90% of the XTEN sequence consists of sequence motifs that do not overlap , the sequence reasons being selected from the group consisting of the sequences established in Table 1； (b) the sum of glycine (G), alanine (A), serine (S), threonine (T), glutamate (E) and proline (P) residues constitutes more than 90% of the total amino acid sequence of XTEN ； (c) the XTEN sequence is substantially non-repetitive because none of the three contiguous amino acids in the sequence are types of identical amino acids unless the amino acid is serine, in which case no more than three contiguous amino acids are serine residues； (d) the XTEN sequence lacks a predicted T lymphocyte epitope when analyzed by the TEPITOPE algorithm, where the TEPITOPE prediction algorithm for epitopes within the XTEN sequence is based on a score of -6 or higher； (e) the XTEN sequence has a random curl formation of more than 90% as determined by the Garnier-Osguthorpe-Robson algorithm； and (f) the XTEN sequence has less than 2% alpha helices and 2% beta sheets as determined by the Chou-Fasman algorithm.Un polipeptido recombinante extendido (XTEN) aislado que comprende mas de 100 a 3000 restos de aminoacidos, en donde el XTEN se caracteriza por que: (a) al menos el 90 % de la secuencia de XTEN consiste en motivos de secuencia que no se solapan, seleccionandose los motivos de secuencia entre el grupo que consiste en las secuencias establecidas en la Tabla 1； (b) la suma de restos de glicina (G), alanina (A), serina (S), treonina (T), glutamato (E) y prolina (P) constituye mas del 90 % de la secuencia de aminoacidos total del XTEN； (c) la secuencia de XTEN es sustancialmente no repetitiva por que ninguno de los tres aminoacidos contiguos en la secuencia son tipos de aminoacidos identicos a menos que el aminoacido sea serina, en cuyo caso no mas de tres a
