Abstract: Friction disks of a clutch are axially positioned and supported relative to the drum of the clutch, using a tapered snap ring. Furthermore, an engaging member coupled with a ring gear is axially positioned and supported by sandwiching between the tapered snap ring and another snap ring. Accordingly, the structure accommodates and supports receipt of hydraulic pressure, as well as thrust force of the ring gear.

Abstract: A method for performing site-directed mutagenesis characterized in that the method includes the step of carrying out PCR by the use of a double-stranded DNA vector having one or more amber codons, the vector resulting from insertion of a target DNA fragment for site-directed mutagenesis, and at least two kinds of selection primers; and a kit for site-directed mutagenesis for use in the above method, characterized in that the kit includes amber codon reversion primers. According to the present invention, there can be provided a method for performing site-directed mutagenesis and a kit, which is useful for genetic engineering or protein engineering, more simply and rapidly. By using the method and the kit of the present invention, it is possible to efficiently obtain a mutation-introduced gene at the desired position by simply transforming a host with a PCR product obtained by PCR.