Proline-rich proteins are among the major protein components of plant cell walls, and the different gene families identified so far display cell type specific expression patterns. So far, three different proline rich putative cell wall proteins have been described in maize. We now report the identification of two additional proteins, tentatively designated HRGP4 and HRGP5, the amino acid sequence of which has been deduced in the case of HRGP4 from the nucleic acid sequence of a cDNA isolated from a leaf cDNA-library, and in the case of HRGP5 from the sequence of a gene isolated from a (fixII genomic library. A schematic representation of the structure of the two isolates is given in the Figure. Both protein structures display at their amino-terminus an export specific signal sequence which correlates often with the transport of the proteins into the cell wall. The second domain of HRGP4 from amino acid 152 to 481 is composed of 5 very similar proline-rich repeats consisting largely of proline, lysine and histidine. The central part of these repeats (indicated by the stippled boxes) is almost identical with the main part of the second proline rich protein (dark stippled part) which contains the amino acid sequence block proline-glutamate-proline-lysine repeated 45 times. A particular role of the new proteins in specific cell wall complexes is anticipated and currently under investigation.
 

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