A, Features of MALT1, API2, and the fusion proteins API2-MALT1 and MALT1-API2. Indicated is the domain content (solid bars) of the API2-MALT1 fusion variants A7M3, A7M5, A7M8 and A7M9 (fusion API2 exon 7 to MALT1 exon 3/5/8/9, respectively) and their corresponding MALT1-API2 fusion variants M2A8, M4A8, M7A8 and M8A8 (fusion MALT1 exon 2/4/7/8, respectively, to API2 exon 8). B, Shown are the amplification products of nested PCR reactions on cDNA extracted from 14 t(11;18)(q21;q21)-positive MALT lymphoma cases (see Table 1). A PCR on pcD-F-M2A8, pcD-F-M4A8 and/or pcD-F-M8A8 was performed as positive control, as indicated. An RT-PCR for MALT1 and GAPDH was included for RNA quality control. C, Results of quantitative RT-PCR for cases 11 and 12 for MALT1-API2, API2-MALT1 and HPRT1. For primers used, see Materials and Methods and Table 2.