Identification of SPI-CI from CMT93. (A) Total RNA of a CTL clone (line 5) and CMT93 was hybridized on Northern blot with a probe spanning the coding sequence of SPI-6 (left panel). As compared with the CTL clone, an additional band is detected in CMT93 (X). To confirm the expression of SPI-CI in CMT93, Northern blots were incubated with either a probe against the 3′UTR of SPI-6 or a probe against the 3′UTR of SPI-CI (middle and right panels, respectively). (B) Alignment of SPI-CI and SPI-6 DNA sequences. The DNA sequence of SPI-CI shares 80% homology (shaded base pairs) with the DNA sequence of SPI-6. Arrows indicate the start and end of the coding sequence. (C) Alignment of the amino acid sequences of SPI-CI and SPI-6. SPI-CI shows 76% identity (shaded amino acids) with SPI-6. The RCL is boxed. (D) Reactive center loop of SPI-CI, SPI-6, and their predicted amino acid at the P1 position.