The inclusion of the alcohol dehydrogenase 1-S(Adh 1-S) intron 1 in the transcription unit of maize gene constructs has been shown to increase gene expression in cultured maize cells. We have extended these studies with Adh1-S intron 1 using the firefly luciferase, Escherichia coli beta-glucuronidase and chloramphenicol acetyltransferase reporter genes adjoined to different plant promoters and find enhancement of transient gene expression in all cases but one. We also show that the enhancement phenomenon can be mediated by the third intron of the maize actin gene. In all cases tested, the inclusion of an intron results in increased levels of steady-state RNA. The degree of enhancement depends on the exon sequences flanking the intron; flanking exons also influence the efficiency of intron splicing. Unexpectedly, unspliced RNAs accumulate during the transient assay.

Pseudomonas aeruginosa is an opportunistic pathogen that can cause acute lung injury and mortality through the delivery of exotoxins by the type III secretion system (TTSS). PcrV is an important structural protein of the TTSS. An engineered human antibody Fab fragment that binds to the P. aeruginosa PcrV protein with high affinity has been identified and has potent in vitro neutralization activity against the TTSS. The instillation of a single dose of Fab into the lungs of mice provided protection against lethal pulmonary challenge of P. aeruginosa and led to a substantial reduction of viable bacterial counts in the lungs. These results demonstrate that blocking of the TTSS by a Fab lacking antibody Fc-mediated effector functions can be sufficient for the effective clearance of pulmonary P. aeruginosa infection.

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Intron recognition in Angiosperms is hypothesized to require AU-rich motifs within introns. In this report we examined the role of AU-rieh motifs in pre-mRNA processing. AU-rich segments of maize introns inserted near the single intron of the maize Bronze-2 (Bz2) gene result in alternative splicing. Other insertions of AU-rich sequence in the Bz2 eDNA resulted in de novo intron creation using splice junctions at the edges of the AU-rich region. Surprisingly, the five AU-rieh inserts that we tested also caused polyadenyation, even though none had been selected for that function in plants. Insertions of GC-rieh sequence into Bz2 did not cause either splicing or polyadenylation. We propose that AU-rich motifs are a general signal for RNA processing in maize and that in the absence of a 5' splice site, polyadenylation is the default pathway.