The present invention is directed to an exhaust gas treatment system and method for removing particulate matter and nitrogen oxides from diesel engine exhaust streams. More specifically, the present invention relates to an emission treatment system that effectively provides simultaneous treatment of the particulate matter, as well as the NOx and other gaseous components of diesel engine exhaust. The emission treatment system uses an integrated soot filter coated with a catalyst washcoat composition comprising sub-micron particles, thereby providing an ultra-thin sub-micron washcoat layer showing improved catalyst performance without causing excessive backpressure.