The invention is directed to novel promoters or mutants thereof from
Chlorella virus DNA methyltransferase genes. A Chlorella virus gene
promoter is operably linked to a first and/or second DNA sequence encoding
a gene that is different from the Chlorella virus gene to form an
expression cassette. An expression cassette can be introduced into
prokaryotic and/or eukaryotic cells and can provide for a high level of
expression of the gene encoded by the first and/or second DNA sequence.
The invention also provides a method for screening other Chlorella virus
genes for promoters that can function to express a heterologous gene in
prokaryotic and/or eukaryotic hosts.