Non-silencing selectable marker genes and methods of use

An expression vector for transgene expression in eukaryotic cells, comprising:

• (a) an expression cassette comprising a transgene operably linked to a promoter functional in eukaryotic cells;
• and
• (b) a non silencing selectable marker gene that provides drug resistance for prokaryotic cells, wherein the non silencing selectable marker gene comprises a nucleotide sequence that (i) encodes a drug selectable marker protein;
• (ii) is operably linked to a promoter functional in prokaryotic cells, and (iii) comprises an A/T content in a range of from 52% to 70%.

A nucleic acid encoding a drug selectable marker protein, comprising:

• a nucleotide sequence encoding a drug selectable marker protein, wherein:
• (i) the nucleotide sequence has 87% or more sequence identity with the nucleotide sequence set forth in SEQ ID NO:
• 4 and the encoded drug selectable marker protein provides resistance to kanamycin;
• or
• (ii) the nucleotide sequence has 88% or more sequence identity with the nucleotide sequence set forth in SEQ ID NO:
• 13 and the encoded drug selectable marker protein provides resistance to ampicillin;
• or
• (iii) the nucleotide sequence has 73% or more sequence identity with the nucleotide sequence set forth in SEQ ID NO:
• 29 and the encoded drug selectable marker protein provides resistance to tetracycline.