1. A method of preparing a compound produced by a protein encoded by the gene or genome sequence of the presumed gene containing an intron by using an expression vector prepared by a method of preparing an expression vector by linking exon sequences of a eukaryotic gene containing an intron or from the genome sequence of a presumed eukaryotic gene containing an intron to form the expression vector containing the linked sequences, said method comprising the steps of: (a) amplifying exon sequences from a genome extracted from a eukaryote by PCR to prepare multiple fragments, wherein the forward primer used in the PCR has, in order from the 5′ end to the 3′ end, a sequence complementary to the sequence of the 3′ terminal part of the sense strand of a fragment to which the amplified fragment is to be linked, or a sequence complementary to the sequence of the 3′ terminal part of the sense strand of a restriction enzyme-treated terminal part of the vector, and a sequence complementary to the sequence of the 5′ terminal part of the sense strand of the fragment to be amplified, and wherein the reverse primer has, in order from the 5′ end to the 3′ end, a sequence complementary to the sequence of the 3′ terminal part of the antisense strand of a fragment to which the amplified fragment is to be linked, or a sequence complementary to the sequence of the 3′ terminal part of the antisense strand of a restriction enzyme-treated terminal part of the vector, and a sequence complementary to the sequence of the 5′ terminal part of the antisense strand of the fragment to be amplified, whereby a sequence homologous to a terminal part of a fragment to be linked to the fragment to be amplified or a sequence homologous to a restriction enzyme-treated terminal part of the vector are added to the end of the fragment to be amplified; and (b) simultaneously transforming a budding yeast or fission yeast with the fragments obtained in the step (a) and a restriction enzyme-treated vector to obtain the expression vector containing fragments linked to the fragments and fragments linked to the vector that are joined via homologous recombination, wherein the gene or genome sequence of the presumed gene encodes a polyketide synthase gene or nonribosomal peptide synthetase gene, and wherein the linked sequence is a polynucleotide comprising the nucleotide sequence of SEQ ID NOs:15 to 21, 29 or 47.