By this invention, novel nucleic acid sequences encoding for acyl-CoA: cholesterol acyltransferase (ACAT) related proteins are provided, wherein said ACAT-like protein is active in the formation of a sterol ester and/or triacylylgycerol from a fatty acyl-CoA and sterol and/or diacylglycerol substrates. Also considered are amino acid and nucleic acid sequences obtainable from ACAT-like nucleic acid sequences and the use of such sequences to provide transgenic host cells capable of producing sterol esters and/or triacylglycerols.