Who was she?
In Cleveland, Ohio 1927, Martha Cowles Chase was born. She grew up in Ohio with her family, including her father Samuel Chase - a science instructor at Western Reserve University. Potentially inspired by her father's work, she graduated from the College of Wooster with a bachelor's degree in 1950 and continued her studies at the University of Southern California 9 years later. This led to her completing her PhD in Microbiology in 1964. However, her most notable work occurred in the years between her studies when working as a research assistant under Alfred Hershey.
The Hershey-Chase experiments
In 1952, Alfred Hershey set out to prove that protein is not hereditary material with the help of Martha Chase, using bacteriophage T2.
The structure of 'phage T2
DNA is tightly packed inside an icosahedral head attached to a core, which is surrounded by a sheath that is terminated by a base plate from which tail fibres emerge.
The state of 'phage T2 research 1948-1952
The T2 'phage infects E. coli, with attachment mediated by the base plate and fibres. After infection, 'phage particles remain attached to the bacterium but the heads appear empty forming ghosts. The E. coli then lyse and release new virions. T2 ‘phages were known to consist of both protein and DNA in approximately equal amounts but the role each substance played in infection was unknown. To trace the fate of ‘phage protein and DNA, Chase used differential radioactive labelling.
Differential labelling
Sulphur (35S) is present in proteins (methionine and cysteine amino acids) but not in DNA. Phosphorus (32P) is present in large amounts in nucleic acids but generally not in proteins (although some can be phosphorylated). Chase used this labelling to track DNA and protein in the experiments.
Labelling of 'phage DNA
First, they infected E. coli cells with T2 ‘phages and grew them in medium containing 32P and 35S. Then, they waited until they had 'phage "ghosts". The cells then lysed and released viral virions which they centrifuged. The living and lysed bacteria were discarded and ’phage suspension was collected, this contained DNA and protein labelled ‘phages.
1952: the Hershey-Chase experiments
They infected E.Coli with labelled ‘phages and waited long enough for "ghosts" to form. Next they knocked of the "ghosts" by putting the whole culture into a waring blender. They centrifuged the material to make the infected and uninfected bacteria separate to the bottom and ghosts to the top. They took the infected and uninfected bacteria and found some bacteria were labelled with 32P. They grew these bacteria in fresh media and some of the viral progeny were 32P labelled yet not 35S labelled. This meant that the 32P starts in DNA of the 'phage and gets passed into the E. coli, then some of the infected bacteria had labelled progeny, meaning the DNA (and not protein) had been passed down a generation and is hereditary material.
Hershey could not state that their experiments showed that DNA was the genetic material and said "The DNA has found some function. Further chemical inferences should not be drawn from the experiments presented“ as he was cautious to interpret the data. This meant that for many years scientists didn’t believe that DNA was genetic material. Despite this, Hershey shared a Nobel prize in 1969 with Delbruck and Luria (for their discoveries concerning the replication mechanism and genetic structure of viruses).
Why was Chase crucial to Hershey's experiments?
There exists limited information regarding the extent of Chase's "intellectual contribution" to the experiment. However, it's worth noting that she was designated as a co-author on the research paper, a departure from the typical practice due to her role as a research assistant. This suggests a significant involvement on her part and is indicative of her potentially pivotal role in the endeavour.
Yet she was overlooked...
The Nobel Prize awarded to Hershey for Physiology or Medicine in 1969 excluded Martha Chase's work on the experiment. Additionally, Hershey didn’t mention Chase in his acceptance speech (which was hours long!) and she got little to no credit for the huge amount of work that she did for Hershey.
Women in science - the bigger picture.
This makes Martha Chase just one example of how women in science have been and are still being overlooked. Women in STEM have historically faced significant challenges that have led to their underrepresentation and insufficient recognition. These challenges include implicit biases that perpetuate the perception of men as more competent in scientific domains, resulting in the downplaying or oversight of women's contributions. The lack of women in leadership positions and decision-making roles contributes to the inadequate consideration and valuation of their perspectives and input. Moreover, publication bias and unequal access to funding, mentorship, and career advancement opportunities can diminish the visibility and impact of women's scientific work.
How can we prevent this in future?
Promoting gender equality in science necessitates a multi-faceted approach. To create a more balanced landscape, it's crucial to encourage girls' interest in STEM from an early age, provide diverse role models, and offer bias awareness training for educators and professionals. Inclusive curricula should be developed to recognize contributions from women and underrepresented groups. Achieving gender parity in leadership, transparent hiring and promotion processes, and addressing pay disparities are vital. With organisations such as the Association for Women in Science (AWIS), 500 Women Scientists and the UNESCO - STEM and Gender Advancement we can hopefully move forward into a world where women feel empowered to pursue scientific endeavours, without fear of discrimination and avoid stories, such as Martha's, repeating themselves.