The present invention provides synthetic 5'UTRs comprising a first polynucleotide fragment and a second polynucleotide fragment, wherein the first polynucleotide fragment comprises at least one splice site of a first eukaryotic gene, the second polynucleotide fragment comprises at least a portion of 5' untranslated region of a second eukaryotic gene, and the first polynucleotide fragment is located 5' of the second polynucleotide fragment. In one embodiment, the first polynucleotide fragment comprises the second intron of a sarcoplasmic/endoplasmic reticulum calcium ATPase gene and the second polynucleotide fragment comprises at least a portion of the 5' untranslated region (5'UTR) of a eukaryotic casein gene. The synthetic 5'UTRs are useful for increasing the expression of a transgene when positioned between a promoter and a transgene within an expression vector. The present invention also provides vectors comprising synthetic 5'UTRs and methods for increasing the expression of a transgene using synthetic 5'UTRs.
