The present invention relates to nucleotide sequences, which are variants of att recombination sequences, involved in sequence-specific recombination of DNA in eukaryotic cells, whereby sequence specific recombination is performed by a bacteriophage lambda integrase Int. Such att recombination sequences being e.g. attP.b, attP.a, attL.a, attR.a and attR.b. The present invention further relates to a method of sequence-specific recombination of DNA in eukaryotic cells, comprising the introduction of a first DNA comprising a nucleotide sequence containing at least one recombination sequence into a cell, introducing a second DNA comprising a nucleotide sequence containing at least one further recombination sequence into a cell, and performing the sequence specific recombination by a bacteriophage lambda integrase Int, whereby at least one of said first or second DNAs is an att recombination sequence being e.g. attP.b, attP.a, attL.a, attR.a or attR.b.