Focused libraries of genetic packages

A focused library of vectors or genetic packages, the focused library comprising vectors or genetic packages which are characterized by variegated DNAs, each of which comprises a sequence that encodes a human antibody heavy chain comprising a synthetic heavy chain CDR1, CDR2 and CDR3,

• wherein the human antibody heavy chain comprises a human heavy chain variable region, wherein the heavy chain variable region consists of a sequence represented by the formula V::nz::D::ny::JHn, wherein V is a v gene, nz is a series of bases that are essentially random, D is a D segment, ny is a series of bases that are essentially random, and JHn is one of the six JH segments;
• wherein the v gene is 3-23, 4-34, 3-30, 3-30.3, or 4-30.1;
• wherein JH is JH4 or JH3;
• wherein the CDR1 segments encoded by the variegated DNAs comprise CDR1 segments that consist of a length of 5 amino acid residues;
• wherein the CDR2 segments encoded by the variegated DNAs comprise CDR2 segments that consist of a length of 17 amino acid residues;
• wherein the CDR3 segments encoded by the variegated DNAs comprise an embedded human antibody heavy chain D segment, wherein the CDR3 segments consist of a length of 7-15 amino acid residues between YYCAR and WG;
• wherein the CDR3 segments in the library comprise amino acid sequence variation and amino acid length variation;
• wherein the variegation is focused so as to closely mimic the naturally-occurring diversity of the specific family that the library represents, both in sequence and in length.