Kaji Research

Contact

Name: Hideko Kaji, PhD
Position: Professor

1020 Locust Street
JAH 456A
Philadelphia, PA 19107

Telephone: 215-503-6547
Ribbon
  • Mechanism of protein biosynthesis with emphasis on the last step: the ribosome recycling step.
  • Post-translational modification of protein by arginine transfer enzyme (discovered by H. Kaji).

This laboratory is studying the last step of protein biosynthesis, ribosome recycling step. This step in bacteria was discovered in the Kaji lab in 1970. It took long time to be accepted by scientific community. However, now most of biochemistry text book describes this step as one of the four steps of protein synthesis, initiation, elongation, termination and the ribosome recycling.  In bacteria, this step is catalyzed by two protein factors, elongation factor G and ribosome recycling factor (RRF). RRF is dedicated solely to catalyze the last step. It is one of the essential bacterial factors on which bacterial life is dependent. We originally named this factor as ribosome releasing factor because we discovered that RRF’s major function is to recycle ribosome by releasing spent mRNA to recycle the ribosome for new round of protein synthesis. Other laboratories used short mRNA with the Shine Dalgarno (SD) sequence to study the RRF reaction. With these mRNAs, due to the strong affinity of the SD sequence to ribosomes, the ribosomes released by RRF from mRNA quickly binds back to mRNA hiding the main function of RRF to release mRNA. Because RRF has two more functions, release of tRNA and splitting of 70S ribosomes into subunits, other laboratories were misled to the wrong conclusion that RRF’s main function is to split 70S ribosomes to get ready for the initiation step. This wrong concept was widely accepted because of the common wrong concept that the initiation of protein synthesis must involve subunits. As a matter of fact, there are two pathways of the initiation of protein synthesis, one involving the subunits, and the other involving 70S ribosomes.   They are equally important but the one involving subunits are more widely accepted.  We feel that it is our responsibility to correct these wrong concept especially because we discovered RRF and initiated the concept of ribosome recycling. We currently use fast kinetic and fluorescent labeled mRNA closely similar to natural mRNA.  Besides these basic studies, we recently developed a new assay system to look for inhibitors to RRF. This work could lead to new antibiotics.

In addition, we are planning to re-start extension of our original observation that the AT enzyme catalyze the protein modification. Our special interest is focused on the possible relation between cognitive diseases and the AT enzyme.

Research Projects

  1. Mechanism of ribosome recycling factor (RRF).
    Correcting general misconception.
  2. Search for a specific inhibitor of RRF
  3. eEF-3 (eukaryotic elongation factor)
  4. Arginine transfer from arginyl-tRNA to a preformed protein.
    Its role in developing cognitive disease.